early 15c., of persons, "emaciation;" of diet, "reduction," from Latin attenuationem (nominative attenuatio) "a lessening," noun of action from past-participle stem of attenuare "to make thin, lessen, diminish," from assimilated form of ad "to" (see ad-) + tenuare "make thin," from tenuis "thin," from PIE root *ten- "to stretch." General sense of "a making less dense" is from 1590s; specifically of electrical currents by 1838.
