Learn Hardcore Indonesian: Dia mencium ibunya. - He/She kisses his/her mother.

Dia means he or she. Indonesian does not normally mark gender in third-person singular pronouns, so the sentence itself does not tell you whether the person is male or female.

Also, dia does not change form like English he/him or she/her. In this sentence, it is the subject: Dia = the person doing the action.

Why is it mencium and not just cium?

The base word is cium, which is related to kiss or smell.

The form mencium uses the prefix meN-, which commonly makes an active verb in standard Indonesian. Because the root begins with c, meN- becomes men-, giving mencium.

So:

cium = root
mencium = to kiss / to smell, as an active verb

In standard written Indonesian, mencium is the expected form here.

Does mencium only mean to kiss?