amniotic (adj.)

"innermost membrane around the embryo of a higher vertebrate" (reptiles, birds, mammals), 1660s, Modern Latin, from Greek amnion "membrane around a fetus," originally "vase in which the blood of a sacrifice was caught," which is of unknown origin; sometimes said to be from amē "bucket," or a diminutive of amnos "lamb."

Middle English -ik, -ick, word-forming element making adjectives, "having to do with, having the nature of, being, made of, caused by, similar to," from French -ique and directly from Latin -icus or from cognate Greek -ikos "in the manner of; pertaining to." From PIE adjective suffix *-(i)ko, which also yielded Slavic -isku, adjectival suffix indicating origin, the source of the -sky (Russian -skii) in many surnames. In chemistry, indicating a higher valence than names in -ous (first in benzoic, 1791).

In Middle English and after often spelled -ick, -ike, -ique. Variant forms in -ick (critick, ethick) were common in early Modern English and survived in English dictionaries into early 19c. This spelling was supported by Johnson but opposed by Webster, who prevailed.

1880, "without an amnion" (of amphibians and fishes); see an- (1) "not, without" + amniotic.