"orifice of communication between the stomach and intestines," 1610s, from Late Latin pylorus "the lower orifice of the stomach," from Greek pylōros "lower orifice of the stomach," literally "gatekeeper, porter," from pylē "gate" (see pylon) + ouros "watcher, guardian" (from PIE root *wer- (3) "perceive, watch out for"). Related: Pyloric.
"lower part of the alimentary canal," early 15c., from Old French intestin (14c.) or directly from Latin intestinum "a gut," in plural (intestina), "intestines, bowels," noun use of neuter of adjective intestinus "inward, internal," from intus "within, on the inside" (from PIE *entos, suffixed form of root *en "in").
Distinction of large and small intestines in Middle English was made under the terms gross and subtle. Intestine also was used as an adjective in English 16c.-19c. with a sense (as in French) of "internal, domestic, civil."