1891, short for Martini cocktail (1886), perhaps from Martini & Rossi, Italian firm that makes vermouth (an ingredient of the drink); the firm was in existence then by that name, but it is not specified among the ingredients in the earliest recipes (such as Harry Johnson's "Bartender's Manual," 1888). Another theory holds that it is a corruption of Martinez, California, the town where the drink was said to have originated. See discussion in Lowell Edmunds' book "Martini, Straight Up" (1998).
As the name of a type of rifle used by the British army from 1871 to 1891, it is attested from 1870, from Friedrich von Martini, who invented the breech mechanism on it.
"1 more than two; the number which is one more than two; a symbol representing this number;" Old English þreo, fem. and neuter (masc. þri, þrie), from Proto-Germanic *thrijiz (source also of Old Saxon thria, Old Frisian thre, Middle Dutch and Dutch drie, Old High German dri, German drei, Old Norse þrir, Danish tre), from nominative plural of PIE root *trei- "three" (source also of Sanskrit trayas, Avestan thri, Greek treis, Latin tres, Lithuanian trys, Old Church Slavonic trye, Irish and Welsh tri "three").
3-D first attested 1952, abbreviation of three-dimensional (1878). Three-piece suit is recorded from 1909. Three cheers for ______ is recorded from 1751. Three-martini lunch is attested from 1972. Three-ring circus is recorded by 1898. Three-sixty "complete turnaround" is from 1927, originally among aviators, in reference to the number of degrees in a full circle. Three musketeers translates French les trois mousquetaires, title of the 1844 novel by Alexandre Dumas père.