noun
Standard word for an umbrella used against rain. Contrasts with 日傘 (ひがさ, parasol/sun umbrella).
雨が降りそうだから、雨傘を持って行ったほうがいいよ。
It looks like rain, so you'd better take an umbrella.
Compound of 雨 (あま, rain) + 傘 (かさ, umbrella), with rendaku voicing of かさ to がさ.