*deks-

"faculty of using both hands with equal facility," 1650s, with -ity + Medieval Latin ambidexter, literally "right-handed on both sides," from ambi- "both, on both sides" (see ambi-) + dexter "right-handed" (from PIE root *deks- "right; south").

also ambidexterous, "able to use both hands equally," 1640s, with -ous + Medieval Latin ambidexter, literally "right-handed on both sides," from ambi- "both, on both sides" (see ambi-) + dexter "right-handed" (from PIE root *deks- "right; south"). An earlier English use of ambidexter (adj.) meant "double-dealer, one who takes both sides in a conflict" (late 14c.).

Its opposite, ambilevous "left-handed on both sides," hence "clumsy" (1640s) is rare. Ambidexter as a noun is attested from 1530s (in the sense "one who takes bribes from both sides") and is the earliest form of the word in English; its sense of "one who uses both hands equally well" appears by 1590s.