tactyoudaoicibaDictYouDict[tact 词源字典]
tact: [17] Tact originally denoted the ‘sense of touch’ (that is what Alexander Ross was referring to when he wrote ‘Of all the creatures, the sense of tact is most exquisite in man’, Arcana microcosmi 1651). But by the end of the 18th century it had evolved semantically via ‘refined faculty of perception’ to ‘skill in behaving or speaking with propriety or sensitivity’.

It was acquired via French tact from Latin tactus ‘sense of touch’, a noun use of the past participle of tangere ‘touch’ (source of English contact, tangent, tangible, etc). Tactile [17], from the Latin derivative tactilis, preserves the original notion of ‘touching’.
=> contact, contagion, tactile, tangent, tangible[tact etymology, tact origin, 英语词源]
tact (n.)youdaoicibaDictYouDict
1650s, "sense of touch or feeling" (with an isolated instance, tacþe from c. 1200), from Latin tactus "a touch, handling, sense of touch," from root of tangere "to touch" (see tangent (adj.)). Meaning "sense of discernment in action or conduct, diplomacy, fine intuitive mental perception" first recorded 1804, from development in French cognate tact. The Latin figurative sense was "influence, effect."