mid-14c., "choose, select, pick; collect and gather the best things from a number or quantity," especially with reference to literature, from Old French cuiler "collect, gather, pluck, select" (12c., Modern French cueillir), from Latin colligere "gather together, collect," originally "choose, select" (see collect).
Meaning "select livestock according to quality" is from 1889; notion of "select and kill (animals)," usually in the name of reducing overpopulation or improving the stock, is from 1934. Related: Culled; culling.
1610s, "a selection, something picked out," from cull (v.). From 1791 as "flock animal selected as inferior;" 1958 as "a killing of animals deemed inferior."
1690s, earlier cully (1660s) "a dupe, a sap-head," "a verdant fellow who is easily deceived, tricked, or imposed on" [Century Dictionary], rogues' slang, of uncertain origin.
Perhaps a shortening of cullion "base fellow," originally "testicle" (from French couillon, from Old French coillon "testicle; worthless fellow, dolt," from Latin coleus, literally "strainer bag;" see cojones). Another theory traces it to Romany (Gypsy) chulai "man." Also sometimes in the form cully, however some authorities assert cully was the canting term for "dupe" and cull was generic "man, fellow" without implication of gullibility. Compare also gullible. Related: Cullibility (1728).