Senses
一回事 one and the same thing
one thing; a single matter; often used to emphasize that two situations or topics are identical
一回事 a separate matter
one thing as distinct from another; used in pairs to emphasize that two things are unrelated or different in nature
一回事 a situation
a matter; an occurrence; what is going on
一回事 a significant matter
something important; something taken seriously, often used in the negative to mean 'not a big deal'