"Ọ riri nri." - kedu ụdị okwu 'riri'?

The sentence O riri nri means "He/she ate food." To identify the part of speech (udu okwu) of riri, we examine its function in the sentence.

Riri is the past tense form of the verb iri (to eat). In Igbo grammar, verbs (ngwaa or vob) are words that express actions, states, or occurrences. In this sentence, riri expresses the action of eating that the subject (o) performed. The reduplication of the root ri to form riri is a standard Igbo past tense verb formation pattern.

The word is not a noun (aha), which names a person, place, or thing. It is not a question word (ajuju). It is not a directive or adverb (ntuzika). It is a vob (verb) - it tells us what the subject did.