"secreting internally,"

endo- + Latinized form of Greek krinein "to separate, distinguish".

certain (adj.)

c. 1300, "determined, fixed," from Old French certain "reliable, sure, assured" (12c.), from Vulgar Latin *certanus, extended form of Latin certus "determined, resolved, fixed, settled," of things whose qualities are invariable, "established," also "placed beyond doubt, sure, true, proved; unerring, to be depended upon" (also source of Old French cert, Italian certo, Spanish cierto), originally a variant past participle of cernere "to distinguish, decide," literally "to sift, separate." This Latin verb comes from the root *krei- "to sieve," thus "discriminate, distinguish.”

1917, from endocrine + -ology. Related: Endocrinologist.

endorse (v.)

c. 1400, endosse "confirm or approve"

endow (v.)

late 14c., indowen "provide an income for," from Anglo-French endover, from en- "in" + Old French douer "endow," from Latin dotare "to endow, bestow, portion," from dos (genitive dotis) "marriage portion."

"growing or proceeding from within," especially with reference to a class of plants including cereals, palms, plantains, etc., 1822, from endo- "within" + -genous "producing."

"chemical which occurs naturally in the brain and works like morphine," 1975, from French endorphine. First element from endogène "endogenous, growing within."

"lining membrane of the uterus," 1882, medical Latin, from endo- + Greek mētra "uterus," related to mētēr "mother" (see mother (n.1)). Related: Endometrial (1870).

1838, from endo- + skeleton.

ENDOSCOPY

endo-

word-forming element meaning "inside, within, internal," from Greek endon "in, within."

-scopy

word-forming element meaning "viewing, examining, observing," from Modern Latin -scopium, from Greek -skopion, from skopein "to look at, examine."