noun
A mildly derogatory term for a foolish, slow-witted, or lazy person. Often used in casual, colloquial speech. The prefix うすら- adds a nuance of 'somewhat' or 'a bit', softening the insult compared to 馬鹿 alone.
あいつはうすらばかだから、何を言っても無駄だ。
That guy is a dimwit, so it's no use saying anything to him.
うすらばかなことを言うなよ。
Don't say such stupid things.
Derived from the prefix うすら (meaning 'slight' or 'somewhat') attached to 馬鹿 (fool). The exact historical origin of うすら is uncertain, but it is related to 薄い (thin, weak).