Apparently by transposition for kebes; a young sheep -- lamb.
see HEBREW kebes
H3775. keseb
כֶּ֫שֶׂב noun [masculine] lamb (transposed from preceding) — ׳כ absolute Leviticus 3:7 5t.; plural כְּשָׂבִים Genesis 30:32 6t.; — lamb, as property 30:32-33, 35, 40 (J); for sacrifice Leviticus 1:10; 3:7; 4:35; 22:19; Numbers 18:17, compare Leviticus 22:27; for food 7:23, compare 17:3 (all P); Deuteronomy 14:4.