Learn Hardcore Finnish: Sunnuntai-iltana lepään kotona ja katson elokuvaa. - On Sunday evening I rest at home and watch a movie.

The hyphen shows that sunnuntai (Sunday) and ilta (evening) form one compound noun: sunnuntai-ilta = Sunday evening. Then the ending -na is added to the compound as a whole: sunnuntai-ilta → sunnuntai-iltana.

In Finnish, days of the week are normally written with a lowercase first letter (maanantai, tiistai, sunnuntai), but here Sunnuntai-iltana is at the beginning of the sentence, so it is capitalized for that reason only (sentence-initial), not because it is a day name.

What exactly does the -na ending in Sunnuntai-iltana mean?

The -na / -nä ending is the essive case. One of its common uses is to express time in the sense of “on / during X (time)”:

maanantaina = on Monday
iltana = in the evening / on (that) evening
sunnuntai-iltana = on Sunday evening

So Sunnuntai-iltana literally means something like “as Sunday evening”, which corresponds idiomatically to “on Sunday evening” in English.

Is Sunnuntai-iltana the only way to say “on Sunday evening”? Could I say it differently?

You can say it in a few natural ways, for example:

Sunnuntai-iltana lepään kotona… (as in your sentence)
Sunnuntaina illalla lepään kotona… – literally “on Sunday in the evening”
Sunnuntai-iltasin lepään kotona… – “on Sunday evenings (habitually) I rest at home…”

So Sunnuntai-iltana is one compact, idiomatic way to express “on Sunday evening”, but not the only possible one.

What form is lepään, and what is the basic dictionary form of this verb?

Lepään is:

person: 1st person singular (“I”)
tense: present
mood: indicative
verb: levätä = “to rest”

The present-tense forms of levätä are a bit irregular:

minä lepään – I rest
sinä lepäät – you rest
hän lepää – he/she rests
me lepäämme – we rest
te lepäätte – you (pl.) rest
he lepäävät – they rest

So the dictionary form is levätä, but in the present you mostly see the stem lepää- / lepä-.

What does kotona mean exactly, and how is it related to koti, kotiin, and kotoa?

All of these are forms of koti (“home”):

koti – home (basic form)
kotona – at home (location, “inside/at home”)
kotiin – (to) home (movement towards home)
kotoa – from home (movement away from home)

In your sentence, lepään kotona = “I rest at home”.

Grammatically, kotona is an irregular inessive form (“in/at”), but for a learner it’s fine to just memorize it as a fixed word meaning “at home”.

What form is katson, and what’s the basic verb?

Katson is:

person: 1st person singular (“I”)
tense: present
mood: indicative
verb: katsoa = “to watch / to look”

Present forms:

minä katson – I watch / I look
sinä katsot – you watch
hän katsoo – he/she watches
me katsomme – we watch
te katsotte – you (pl.) watch
he katsovat – they watch

Why is it elokuvaa and not elokuva or elokuvan?

Elokuvaa is the partitive singular of elokuva (“movie, film”).

Finnish often uses the partitive object when:

the action is ongoing / incomplete or not viewed as a finished whole
you’re talking about an indefinite or “unspecified amount” of something

Katson elokuvaa can be understood as:

“I’m (in the process of) watching a movie / some movie.”

Compare:

Katson elokuvaa. – I’m watching (a) movie. (activity, ongoing)
Katson elokuvan. – I (will) watch the whole movie / I watch the movie (to its end). (more whole/complete event)

So elokuvaa gives a more neutral, “I’m watching a movie” feel, without focusing on completion.

How would the meaning change if I said katson elokuvan instead of katson elokuvaa?

Katson elokuvan uses the genitive object (elokuvan) and usually presents the action as a bounded, complete event:

Katson elokuvan. – I (will) watch the movie (all the way through; I’ll finish it).

In contrast:

Katson elokuvaa. – I watch / I’m watching a movie (emphasis on the activity, not on finishing).

In everyday conversation, this difference can be subtle, but it’s a real aspect contrast in Finnish.

Why is there no word for “a” or “the” in the sentence?

Finnish has no articles like English a / an / the. Nouns stand without them:

elokuva can mean “a movie” or “the movie”, depending on context.
Here, elokuvaa (partitive) is naturally understood as “a movie / some movie”.

Definiteness is usually shown by context, word order, or additional words (like se = “that/it”), not by separate articles.

Can I change the word order, for example: Lepään kotona sunnuntai-iltana ja katson elokuvaa?

Yes. Finnish word order is relatively flexible. All of these are grammatical:

Sunnuntai-iltana lepään kotona ja katson elokuvaa.
Lepään kotona sunnuntai-iltana ja katson elokuvaa.
Sunnuntai-iltana kotona lepään ja katson elokuvaa.

The most neutral, natural order for time expressions is often [time] + [verb] + [place], so your original Sunnuntai-iltana lepään kotona… sounds very typical. Moving elements around can change the emphasis (“It’s on Sunday evening that I rest at home”, etc.), but the basic meaning stays the same.

How would I say “On Sunday evenings I usually rest at home and watch a movie” (habitually)?

You can express a habitual action with the -isin form on the time word:

Sunnuntai-iltaisin lepään yleensä kotona ja katson elokuvaa.

Breakdown:

Sunnuntai-iltaisin – on Sunday evenings (habitually, repeated)
yleensä – usually
lepään kotona ja katson elokuvaa – I rest at home and watch a movie

So Sunnuntai-iltaisin indicates something you regularly do on Sunday evenings.

How would I say this in the past: “Last Sunday evening I rested at home and watched a movie”?

You mainly change the time expression and put the verbs in the past tense:

Viime sunnuntai-iltana lepäsin kotona ja katsoin elokuvaa.

Details:

Viime – last
sunnuntai-iltana – on Sunday evening
lepäsin – I rested (past of lepään)
katsoin – I watched (past of katson)
elokuvaa – a movie (partitive: activity / not stressing completion)