late 14c., from Old French transposer (14c.), from Latin transponere (past participle transpositus) "to place over," from trans- "over" (see trans-) + ponere "to put, place" (see position). Form altered in French on model of poser "to put, place." Sense of "put music in a different key" is from c.1600. Related: Transposed; transposing.