also back-space, 1899, in reference to typewriter keyboards, from back (adv.) + space.

We have had the pleasure of examining one of the 1899 model Hammond typewriters, with the new back-space key. This new feature is certainly an improvement in the machine. [The Phonetic Journal, March 11, 1899]s

also back-stabber, in the figurative sense of "traitorous friend or confidante who attacks when one's back is turned," 1839, from back (n.) + agent noun from stab (v.). The verb backstab in the figurative sense is from 1925. Related: Backstabbing.

also back-stage, "the area of a theater out of view of the audience," especially in the wings or dressing rooms, 1891; see back (adj.) + stage (n.).

"stairs at the back of a structure," 1650s, from back (adj.) + stairs (see stair). Figurative use is attested earlier (1640s).

also back-stitch, 1610s, from back (adj.) + stitch (n.). So called because each stitch doubles back on the preceding one. As a verb from 1720.

1819, "something at the back as a barrier;" see back (adj.) + stop (n.). In U.S. baseball, from 1889, "fence a short distance behind the catcher on a baseball team;" the figurative extension to the catcher himself is by 1890. The verb is attested from 1956 in the sense of "support." Related: Backstopped; backstopping.

"a history or background," especially for a fictional character or situation, c. 1990, from backgroundstory.

"minor street away from a high or main street," mid-15c., from back (adj.), + street. As an adjective often with connotations of secret and illicit.

also back-stroke, 1670s, "counter-punch;" see back (adv.) + stroke (n.). From 1876 as a swimming stroke done face-up in the water, from back (n.).

also back-talk, "impertinent retort," 1833; see back (adv.) + talk (n.). Originally often used in literary attempts at Irish or Scottish idiom. To talk back "answer impudently or rudely" is from 1849.