"characterized by euphoria," 1885, originally with reference to cocaine, from euphoria + -ic. The noun meaning "a drug which causes euphoria" also is from 1885. Euphoriant is from 1946 as a noun, 1947 as an adjective.
1727, a physician's term for "condition of feeling healthy and comfortable (especially when sick)," medical Latin, from Greek euphoria "power of enduring easily," from euphoros, literally "bearing well," from eu "well" (see eu-) + pherein "to carry," from PIE root *bher- (1) "to carry." Non-technical use, now the main one, dates to 1882 and perhaps is a reintroduction. Earlier the word meant "effective operation of a medicine on a patient" (1680s).
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.