Middle English sightlie is attested from mid-15c. but only in the sense "visible;" unsightly is attested in Middle English only as an adverb meaning "invisibly" (late 15c.). Sightly as "pleasing to the eye" is from 1560s. Middle English also had unsighty "difficult or displeasing to look at" (early 15c., from sighty "attractive," late 14c.), also unsightily in the same sense (c. 1400).
c. 1300, undermyne, "render unstable by digging at the foundation," from under + mine (v.1) "dig." The figurative sense "injure by invisible, secret, or dishonorable means" is attested from early 15c. Similar formation in Dutch ondermijnen, Danish underminere, German unterminiren. The Old English verb was underdelfan. Related: Undermined; undermining.
1610s, "a breathing through," a sense now obsolete, from French perspiration (1560s), noun of action from perspirer "perspire," from Latin perspirare "blow or breathe constantly," from per "through" (from PIE root *per- (1) "forward," hence "through") + spirare "to breathe, blow" (see spirit (n.)). Applied by 1620s to "excretion of invisible moistures through the skin," hence its later use as a euphemism for "sweat" (1725).
late 13c., "sound made by the human mouth," from Old French voiz "voice, speech; word, saying, rumor, report" (Modern French voix), from Latin vocem (nominative vox) "voice, sound, utterance, cry, call, speech, sentence, language, word" (source also of Italian voce, Spanish voz), related to vocare "to call" (from PIE root *wekw- "to speak").
Replaced Old English stefn "voice," from Proto-Germanic *stemno, from PIE *stomen- (see stoma). Meaning "ability in a singer" is first attested c. 1600. Meaning "expression of feeling, etc." (in reference to groups of people, etc., such as Voice of America) is recorded from late 14c. Meaning "invisible spirit or force that directs or suggests," (especially in the context of insanity, as in hear voices in (one's) head, is from 1911.