1917, short for medical examination. Earlier it was colloquial for "a student or practitioner of medicine" (1823).
1831 in the sporting sense, "a gathering of huntsmen for fox-hunting," from meet (v.). Later of bicyclists gathering for a ride, etc.
"excuse for being," 1864, first recorded in letter of J.S. Mill, from French raison d'être, literally "rational grounds for existence."
1640s, originally of muscles which raise a part of the body, from Latin elevator "one who raises up," agent noun from past participle stem of elevare (see elevate). As a name for a mechanical lift (originally for grain) attested from 1787. Elevator music for bland, low-volume background music meant to relax listeners is attested by 1963. Elevator as a lift for shoes is from 1940.