"closed end of a passage," 1851 in reference to drainpipes, 1874 in reference to railway lines; by 1886 of streets; from dead (adj.) + end (n.). Figurative use, "course of action that leads nowhere," is by 1914. As an adjective in the figurative sense by 1917; as a verb by 1921. Related: Dead-ended; dead-ending; deadender (by 1996).
also long-shot, in the figurative sense of "something unlikely," 1867, from long (adj.) + shot (n.). The notion is of a shot at a target from a great distance, thus difficult to make. The phrase by a long shot "by a considerable amount," frequently negative, is attested by 1830, American English colloquial. The cinematic sense of the noun phrase is from 1922. As an adjective by 1975.
also Q & A, 1954 (adj.), abbreviation of question and answer (itself attested by 1817 as a noun, by 1839 as an adjective).