noun
plain woman; unattractive woman
A somewhat blunt or old-fashioned noun for a woman who is not considered beautiful. Often used in contrast with 美人. Can sound direct or insensitive in modern conversation.
彼女は自分を不美人だと思っているが、実際はとても魅力的だ。
She thinks of herself as a plain woman, but in reality she is very charming.
昔の小説には「不美人だが気立ての良い娘」といった表現がよく出てくる。
In old novels, you often see phrases like 'a plain but good-natured girl'.
ブス is a very blunt, slang term for an ugly woman, much stronger and more insulting than 不美人. 不美人 is more matter-of-fact and less vulgar.
Formed from the prefix 不 (fu-, 'not') and 美人 (bijin, 'beautiful woman'). The prefix 不 is a common negative prefix borrowed from Chinese.