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.
I woke up with a semi.
I got a semi just from her little gesture.
Formed from 甘い in its sense “incomplete; insufficient” and 勃ち “erection,” denoting an erection that is not fully firm.