scrawny (adj.)

"thin, slight, slender, eager," 1630s; any modern use traces to Milton ("Lycidas," 124), who may have invented it out of dialectal scranny, a variant of scrawny. Or it might have been an existing word from a Scandinavian source akin to Norwegian skran "rubbish." Also compare English dialectal and Scottish skran "scraps, broken victuals; refuse," in military slang "food," which is of obscure origin, hence out on the scran "begging."

early 13c., scraggi, "rough, jagged" (figurative); 1570s, of landscape, "rough, rugged, stumpy;" 1610s, of persons or animals, "gaunt and wasted, lean, thin, bony;" see scrag (n.) + -y (2), and compare scroggy, scraggly, scrawny. In the landscape sense perhaps via scrag in the obsolete sense of "stump of a tree, rough projection from a trunk" (1560s), which had various spellings. In Scottish and Northern English, scranky "lean, slender, scraggy" (18c.). Related: Scraggily; scragginess.