Types

Mostly 3 categories

• Noun
• Verb
• Adjective
• (Particles)
• (Specialized words, e.g. conjunctions)

Word origin: 和語 vs 漢語

Independent of the syntactic category above, vocabulary splits by origin:

• 和語 — native Japanese words (kun’yomi). Take お prefix (お水、お帰り).
• 漢語 — sino-japanese words (on’yomi: 勉強、説明、文化). Take ご prefix (ご連絡). Many are also サ変動詞.

This origin distinction drives the お/ご choice in keigo.