Avus pectinem suum iterum amisit et nunc eum in cubiculo quaerit.

Pecten is the dictionary form, but here it is the direct object of amisit, so it must be in the accusative singular: pectinem.

• nominative: pecten = comb
• accusative: pectinem = comb as the thing being lost or sought

Latin changes noun endings depending on their role in the sentence.

Suum means his own. It refers back to the subject of the clause, which is avus.

So:

• pectinem suum = his own comb

Latin uses suus, sua, suum when the possessor is the subject of the clause.

By contrast, eius would usually mean his or her referring to someone else, not the subject. So pectinem eius would sound more like his comb belonging to another person.

Because it must agree with pectinem.

Pectinem is:

• masculine
• singular
• accusative

So the possessive adjective must also be:

• masculine
• singular
• accusative

That gives suum.

Amisit is perfect tense, meaning he lost or he has lost.

In this sentence, it describes a completed action in the past:

• first, grandfather lost the comb
• now, he is looking for it

So the Latin contrasts:

• amisit = completed past action
• quaerit = present action

Quaerit is present tense and means he looks for, he is looking for, or sometimes he seeks.

The word nunc (now) makes the time especially clear:

• nunc eum in cubiculo quaerit = now he is looking for it in the bedroom

Latin often uses the simple present where English might naturally say is looking for.

Iterum means again.

It modifies amisit, so the sense is:

• he lost his comb again

It tells us this is not the first time it happened.

Eum refers back to pectinem.

Since pectinem is:

• masculine
• singular
• accusative

the pronoun that replaces it is also:

• masculine
• singular
• accusative

So:

• pectinem ... amisit = he lost the comb
• nunc eum ... quaerit = now he is looking for it

Latin, like English, often uses a pronoun to avoid repetition.

Instead of saying:

• Avus pectinem suum iterum amisit et nunc pectinem in cubiculo quaerit

it is more natural to say:

• ... et nunc eum in cubiculo quaerit

That simply means and now he is looking for it in the bedroom.

Because in with the ablative usually expresses location: in, on, at.

Here, in cubiculo means in the bedroom or in the room as a place where the search is happening.

Compare:

• in cubiculo = in the bedroom (location, ablative)
• in cubiculum = into the bedroom (motion toward, accusative)

Since grandfather is looking for the comb in the bedroom, not moving into it, the ablative is used.

No, Latin word order is much more flexible than English word order because the endings show the grammatical roles.

This sentence could be rearranged in several ways and still mean basically the same thing, for example:

• Avus pectinem suum iterum amisit et nunc eum in cubiculo quaerit
• Avus iterum pectinem suum amisit et nunc in cubiculo eum quaerit

The original order is natural and clear, but Latin does not rely on word order as heavily as English does.

Because the verb ending already tells you the subject is he/she/it.

• amisit = he/she/it lost
• quaerit = he/she/it looks for

Since avus is already established as the subject, Latin does not need to repeat he before quaerit. The sentence naturally means:

• Grandfather lost his comb again, and now he is looking for it in the bedroom.

Yes. Cubiculum can mean bedroom, sleeping room, or sometimes just a private room/chamber, depending on context.

In many beginner translations, bedroom is the most natural choice, but room or chamber can also be possible depending on the setting.