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.
"having unequal sides," in mathematics, 1680s, from Late Latin scalenus, from Greek skalenōs "uneven, unequal, odd (numbered)," as a noun, "triangle with unequal sides" (trigōnon skalēnon), from skallein "to chop, hoe, dig, stir up" (compare its derivative, skalops "a mole"), from PIE root *skel- (1) "to cut."