1610s, from French tube (15c.), from Latin tubus "tube, pipe," a word of unknown origin. The London subway was christened the Twopenny Tube by 1900 (H.D. Browne, in the "Londoner" of June 30); tube for "cylindrical railway tunnel" is attested from 1847. The meaning "TV as a medium" is from 1959, short for cathode ray tube or picture tube. Tube top as a women's clothing style is attested from 1972. Tube steak is attested from 1963 as "frankfurter," slang meaning "penis" is recorded by mid-1980s.

"1 more than one, the number which is one more than one; a symbol representing this number;" Old English twa "two," fem. and neuter form of twegen "two" (see twain), from Proto-Germanic *twa (source also of Old Saxon and Old Frisian twene, twa, Old Norse tveir, tvau, Dutch twee, Old High German zwene, zwo, German zwei, Gothic twai), from PIE *duwo, variant of root *dwo- "two."

Two-fisted is from 1774. Two cheers for _____, expressing qualified enthusiasm first recorded 1951 in E.M. Forster's title "Two Cheers for Democracy." Two-dimensional is recorded from 1883; figurative sense of "lacking substance or depth" is attested from 1934.