1934 in publisher's jargon, "books that have been in publication for some time (prior to the current season) and are still in print;" see back (adj.) + list (n.1). As a verb, "to put on the back list," from 1983. Related: Backlisted.
backhanded
backhoe
backing
backlash
backless
backlist
backlog
backorder
backpack
backpedal
backscratcher