Learn Hardcore Romanian: Ei trimit o invitație prietenilor și familiei pentru ziua de naștere a bunicii. - They are sending an invitation to their friends and family for grandmother's birthday.

Ei means “they” (masculine or mixed group). Romanian is a pro-drop language, so the subject pronoun is often optional because the verb ending already shows the person and number.

Ei trimit o invitație… = They send an invitation…
Trimit o invitație… = (They) send an invitation… – also correct, and more natural in many contexts.

You use Ei:

for emphasis (Ei trimit, they are the ones sending it), or
if the subject might be ambiguous from context.

Why is the verb trimit and not something like trimite?

The verb is a trimite = to send. In the present tense:

(eu) trimit – I send
(tu) trimiți – you send (singular)
(el/ea) trimite – he/she sends
(noi) trimitem – we send
(voi) trimiteți – you send (plural)
(ei/ele) trimit – they send

Because the subject is ei (they), you need the 3rd person plural form: trimit.
Trimite is 3rd person singular (he/she sends), so it would not agree with ei.

Why is it o invitație and not un invitație?

Romanian has gender, and invitație is a feminine noun (singular: o invitație, plural: invitații).

Indefinite articles:

un = a/an (masculine & neuter, singular)
o = a/an (feminine, singular)

So:

o invitație = an invitation (feminine)
Using un invitație would be grammatically wrong because the article doesn’t match the noun’s gender.

Why is prietenilor written with -lor at the end? What does that form mean?

The base noun is prieten = friend (masculine).

plural, indefinite: prieteni = friends
plural, with definite dative/genitive ending: prietenilor

-lor is the definite article for plural dative/genitive (for both masculine and feminine).
In this sentence, prietenilor is in the dative case because it is the indirect object (the people who receive the invitation).

So:

prietenilor ≈ to (the) friends / to their friends
The definite article is attached at the end of the noun, not written separately.

Why is it prietenilor și familiei and not something like la prieteni și la familie?

Romanian often uses the dative case (with the ending, no preposition) instead of la + noun for indirect objects in more careful or standard language.

prietenilor și familiei – dative, more standard and natural here
la prieteni și la familie – can be used in speech, but sounds less formal / less precise

So:

Ei trimit o invitație prietenilor și familiei.
= They send an invitation to (their) friends and (their) family.
Here, prietenilor and familiei are both in the dative after the verb a trimite, so no extra preposition is needed.

Why is familiei in that form, and what is the basic noun?

The basic noun is familie = family (feminine).

Its definite forms include:

familia – the family (nominative/accusative, singular)
familiei – to the family / of the family (dative/genitive, singular)

In the sentence, familiei is dative, because it is another indirect object:
o invitație prietenilor și familiei = an invitation to (their) friends and (their) family.

Why is there no article before prietenilor and familiei? In English we say “to the friends and the family.”

In Romanian, the definite article is usually attached to the end of the noun, not placed in front as a separate word.

prieten → prietenilor (to the friends)
familie → familiei (to the family)

So the -lor and -ei endings here already contain the meaning of “the”.
If you added another word for the article, it would be incorrect; Romanian doesn’t use a separate “the” in these cases.

Could the word order be “Ei trimit prietenilor și familiei o invitație” instead? Is that still correct?

Yes, that is also grammatically correct:

Ei trimit o invitație prietenilor și familiei.
Ei trimit prietenilor și familiei o invitație.

Both mean the same thing. The default, neutral order is usually:

verb
direct object (o invitație)
indirect object (prietenilor și familiei)

Putting prietenilor și familiei before o invitație sounds slightly more emphatic on whom they are sending it to, but it is still natural.

What does pentru mean here, and why do we use pentru ziua de naștere?

pentru means “for”. It introduces a purpose or intended occasion.

pentru ziua de naștere = for the birthday

So in full:
…o invitație prietenilor și familiei pentru ziua de naștere a bunicii.
= …an invitation to their friends and family for the grandmother’s birthday.

You need pentru to show that the invitation is for the event of the grandmother’s birthday.

Why is it ziua de naștere and not just ziua?

zi = day
ziua = the day (feminine, definite)
naștere = birth

ziua de naștere literally means “the day of birth”, and is the standard phrase for “birthday.”

If you said only ziua bunicii, that could mean the grandmother’s day (any day associated with her), not necessarily her birthday. de naștere makes it clear that it is a birthday.

What is the role of the little word a in ziua de naștere a bunicii?

The a here is a possessive/genitival article that you put before the possessor when the possessed noun (ziua de naștere) is already definite (ziua has the definite article).

Pattern:

ziua de naștere a bunicii
= the birthday of the grandmother / the grandmother’s birthday

Structure:

ziua de naștere (definite noun phrase)
a
- bunicii (the possessor in the genitive singular feminine)

You generally need a / al / ai / ale + genitive noun/pronoun to show possession when the possessed noun is definite. Here, a is the correct feminine singular form.

Why is it bunicii and not bunica?

The base noun is bunică = grandmother (feminine).

Case forms:

bunica – the grandmother (nominative/accusative singular, definite)
bunicii – of the grandmother / to the grandmother (genitive/dative singular, definite)

In ziua de naștere a bunicii, bunicii is genitive because it expresses possession (whose birthday).
So bunicii = of the grandmother, and that’s why you cannot use bunica here.

Does prietenilor și familiei mean “their friends and family”? Where is the word their?

Yes, in context it usually means “their friends and (their) family.” Romanian often omits a possessive pronoun when it’s clear from context who the owner is.

More explicit versions would be:

prietenilor lor și familiei lor – to their friends and their family
But this is often not necessary and may sound heavy or overly explicit.

The “their” is understood from the context and the fact that they are the ones sending invitations to friends and family; default assumption: it’s their own social circle.

Could I add a pronoun like le: Ei le trimit o invitație prietenilor și familiei? Is that correct?

Yes, that is grammatically correct and quite natural:

Ei trimit o invitație prietenilor și familiei.
Ei le trimit o invitație prietenilor și familiei.

Here:

le is the indirect object pronoun for “to them” (3rd person plural, dative).
prietenilor și familiei is the full noun phrase clarifying who “them” refers to.

Romanian often uses both the pronoun and the full noun phrase (this is called clitic doubling), especially with indirect objects. It can add clarity or emphasis, though it’s not strictly required in this particular sentence.