Other forms: scrawniest; scrawnier
Scrawny is an insulting way to describe someone who's very thin and weak. You might be surprised by how lifting weights transformed your scrawny teammate to a muscular athlete by the end of the season.
The adjective scrawny can describe a small, underweight body but it can also describe anything that's not very big or well-made — a scrawny tree that never gets any taller or fuller or a scrawny audience that disappoints the band because they were expecting a sold-out concert. Scrawny may have come from the Old Norse word skraelna, to shrivel.