Learn Hardcore German: Sie arbeitet ehrenamtlich im Tierheim. - She works as a volunteer at the animal shelter.

Literally, ehrenamtlich comes from Ehre (honor) + Amt (office/position) and means something like “in an honorary capacity” – doing work for the sake of helping, not for pay.

In normal modern use, ehrenamtlich simply means “as a volunteer / unpaid, in a voluntary role”.
So Sie arbeitet ehrenamtlich im Tierheim = She works there as a volunteer / She volunteers at the animal shelter.

What part of speech is ehrenamtlich here? Why not ehrenamtliche or ehrenamtlicher?

Here ehrenamtlich is an adverb describing how she works (she works voluntarily).

Adjective forms would be:
- ein ehrenamtlicher Mitarbeiter – a volunteer (male) worker
- eine ehrenamtliche Mitarbeiterin – a volunteer (female) worker

In those examples, ehrenamtlicher / ehrenamtliche describe a noun and therefore agree in gender, number, and case.

In your sentence, there is no noun after ehrenamtlich, it just modifies the verb arbeitet, so the -lich form without ending is used as an adverb:

Sie arbeitet ehrenamtlich. – She works as a volunteer.

Could I change the word order and say Sie arbeitet im Tierheim ehrenamtlich?

Yes, that is grammatically correct:

Sie arbeitet ehrenamtlich im Tierheim.
Sie arbeitet im Tierheim ehrenamtlich.

Both are fine and mean the same thing.

Subtle tendencies:

The original (ehrenamtlich earlier) slightly emphasizes the way she works (voluntarily).
The alternative (im Tierheim earlier) slightly emphasizes where she works.

But in everyday speech, both are very natural and the difference is minimal.

What is Tierheim, and why is it written as one word and capitalized?

Tierheim is a compound noun:

Tier = animal
Heim = home

So Tierheim literally = “animal home”, i.e. animal shelter.

In German:

All nouns are capitalized: Tierheim (not tierheim).
Many concepts that in English are two words are written as one compound word in German.

Tierheim is a neuter noun:

das Tierheim – the animal shelter
im Tierheim – in the animal shelter

What does im mean, and how is it formed from in dem?

im is a contraction of in + dem:

in dem Tierheim → im Tierheim

German often contracts preposition + definite article:

in dem → im
in das → ins
an dem → am
zu dem → zum
zu der → zur

So im Tierheim literally is “in the animal shelter”, using the dative form dem (because of location).

Why is Tierheim in the dative case here? I thought in can also take the accusative.

The preposition in can indeed take dative or accusative:

Dative = location (where?)
Accusative = direction/movement (where to?)

Your sentence is about a location (where she works), not movement:

Sie arbeitet im Tierheim.
im = in dem → dative → dem Tierheim

If we expressed movement towards the shelter, we’d use accusative:

Sie geht ins Tierheim.
ins = in das → accusative → das Tierheim

Could I also say Sie arbeitet in einem Tierheim? Is there a difference from im Tierheim?

Yes, Sie arbeitet in einem Tierheim is correct and slightly different:

Sie arbeitet im Tierheim.
Often suggests a specific shelter that both speaker and listener know (the local shelter).
Sie arbeitet in einem Tierheim.
Means “in an animal shelter” – some shelter, not necessarily a particular, previously known one.

Both are grammatically correct; choice depends on whether you mean a specific place or just the type of place.

How is sie arbeitet used for both “she works” and “she is working”? Where is the progressive form?

German usually has only one present tense form:

sie arbeitet = she works or she is working, depending on context.

German does not normally use a separate progressive form like English is working. Context, time expressions, or adverbs give the nuance:

Sie arbeitet heute im Tierheim. – She is working at the animal shelter today.
Sie arbeitet ehrenamtlich im Tierheim. – She works there as a volunteer (regularly / generally).

There is a form like Sie ist am Arbeiten, but it’s rare and often sounds dialectal or informal; the normal standard is just sie arbeitet.

How do I know that Sie here means she and not the formal you?

Sie (capital S) can mean:

she (3rd person singular)
you (formal, singular or plural)

You tell from context and verb form:

Sie arbeitet ehrenamtlich im Tierheim.
- Could mean:
  - She works as a volunteer at the animal shelter.
  - or (formal) You work as a volunteer at the animal shelter.

If there is no context, both readings are grammatically possible.
In real use, you usually know from the situation: Are we talking about someone, or to someone politely?

What is the difference between ehrenamtlich and freiwillig?

Both relate to voluntary work, but with different emphasis:

ehrenamtlich
Focuses on an unpaid, usually organized role in some institution (club, association, charity, local government, etc.).
- Sie arbeitet ehrenamtlich im Tierheim. – She has a volunteer role there.
freiwillig
Generally means voluntary / of one’s own free will, not forced.
- Er kommt freiwillig. – He comes of his own free will.
- Sie hilft freiwillig im Tierheim. – She helps at the shelter voluntarily (not out of obligation).

In the context of structured volunteer work, ehrenamtlich is often the more precise, “official-sounding” word.

How would I say “She is a volunteer at the animal shelter” instead of “She works there as a volunteer”?

You can make ehrenamtlich into an adjective with a noun:

Sie ist ehrenamtliche Mitarbeiterin im Tierheim.
She is a volunteer staff member at the animal shelter.

You can also say more simply:

Sie ist Ehrenamtliche im Tierheim. – She is a volunteer at the shelter.
Sie arbeitet als Ehrenamtliche im Tierheim. – She works as a volunteer at the shelter.

Your original sentence with the adverb is still the most straightforward way to say She volunteers at the animal shelter:

Sie arbeitet ehrenamtlich im Tierheim.

Is there a German verb like to volunteer that I could use instead of arbeitet ehrenamtlich?

There is no single everyday verb that matches English to volunteer in this sense.

Natural ways to say it include:

Sie arbeitet ehrenamtlich im Tierheim. – She volunteers at the animal shelter.
Sie engagiert sich im Tierheim. – She is involved / engages herself at the shelter (often implies volunteer work).
Sie hilft im Tierheim. – She helps at the animal shelter (often understood as volunteer help).

A verb volontieren exists in some contexts, but it usually refers to a specific unpaid trainee position (e.g. in journalism), not general volunteering at a shelter, so it would sound wrong here.

How is arbeitet formed from arbeiten, and why is it not just arbeit?

The infinitive is arbeiten (to work).
To form the 3rd person singular present (he/she/it works), you:

Remove -en: arbeit- (stem)
Add the ending -et: arbeitet

So:

ich arbeite – I work
du arbeitest – you work (informal, singular)
er/sie/es arbeitet – he/she/it works
wir arbeiten – we work
ihr arbeitet – you work (informal, plural)
sie/Sie arbeiten – they / you (formal) work

The extra -e- in arbeitet makes pronunciation easier between t and t; that is why the ending is -et, not just -t.

How do you pronounce ehrenamtlich and Tierheim?

Approximate pronunciation (IPA and English hints):

ehrenamtlich
- IPA: /ˈeːʁənˌʔamtlɪç/
- Roughly: EH-ren-amt-likh
  - eh as in say but longer
  - r is the German r (often in the back of the throat)
  - amt like English “umped” without the p
  - final -lich similar to “likh” with a soft German ch sound (like in German ich, not like English k)
Tierheim
- IPA: /ˈtiːɐ̯haɪm/
- Roughly: TEE-er-hyme
  - Tier: long tee- then a short er that almost merges into the next part
  - Heim like English “hime” in time, but with German ei = English eye sound.