moving stairway

1900, Amer.Eng., trade name of an Otis Elevator Co. moving staircase, coined from escalade, a c.1600 borrowing from M.Fr., where it meant "an assault with ladders on a fortification" (from L. scala "ladder") + -ator in elevator. Fig. use is from 1927. Verb escalate is a 1922 back-formation that came into general use with a sense of "raise" after 1959. Escalation in the fig. sense is from 1938, in ref. to the battleship arms race among world military powers.