Numeric
one
1つが通り過ぎたかと思うと、すぐに次の台風が接近する。No sooner has one typhoon passed than the next one approaches. Noun
for one thing
often used in itemized lists
only
after a noun
(not) even
with a verb in negative form
Noun, Adverb (fukushi)
just (e.g. "just try it")
Noun which may take the genitive case particle 'no'
some kind of; one type of
Also written 1つ【ひとつ】、一【ひとつ】