noun
partial erection; semi-erection; slightly aroused
Vulgar slang used among young people to describe a penis that is not fully erect. Often used in casual, locker-room talk.
朝起きたら甘勃ちしてた。
I woke up with a semi.
彼女のちょっとした仕草で甘勃ちしちゃった。
I got a semi just from her little gesture.