1640s, from Italian telescopio (Galileo, 1611), and Modern Latin telescopium (Kepler, 1613), both from Greek teleskopos "far-seeing," from tele- "far" (from PIE root *kwel- (2) "far" in space or time) + -skopos "watcher" (from PIE root *spek- "to observe"). Said to have been coined by Prince Cesi, founder and head of the Roman Academy of the Lincei (Galileo was a member). Used in English in Latin form from 1619.
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.