1620s, from Late Latin defecationem (nominative deficatio), from defecat-, past participle stem of Latin defecare (see defecate). An Old English word for "bowel movement" was arse-gang literally "arse-going."
1570s, "to purify," from Latin defaecatus, past participle of defaecare "cleanse from dregs, purify," from the phrase de faece "from dregs" (plural faeces; see feces). Excretory sense first recorded 1830 (defecation), American English, from French. Related: Defecated; defecating.
defecate def·e·cate (děf'ĭ-kāt')
v. def·e·cat·ed, def·e·cat·ing, def·e·cates
To void feces from the bowels.