na-adjective, noun which may take the genitive case particle 'no', noun
taciturn; reticent; quiet; untalkative
Describes a person who naturally speaks very little; not necessarily shy or unfriendly, just not talkative. Often used as 無口な人.
彼は無口だけど、とても優しい人です。
He is quiet, but a very kind person.
Because I have a taciturn personality, conversations often don't last long.