Now usually citrulline. An α-amino acid (originally isolated from watermelon, Citrullus vulgaris) found widely in living cells as an intermediate in the synthesis of arginine and in the conversion of ammonia to urea.
Systematic name: 2-amino-5-(carbamoylamino)pentanoic acid; NH₂CONH(CH₂)₃CHNH₂COOH.
Late 19th century (in an earlier sense). From scientific Latin Citrullus + -ine, perhaps originally after German Citrullin, †Citrullinum.