The term gambit originates as an Italian wrestling term, and appears to have been in use by chess players in Rome in the mid-sixteenth century. Ruy Lopez learned the term while visiting Rome in 1560, and he introduced it into print in his text the following year (see "Damiano's Gambit"). According to Lopez, gamba means leg, and gambitare means to set traps.
The original English spelling (gambett) was introduced by Gioachino Greco, and is derived from Italian; the modern English spelling derives from Lopez's Spanish. Francis Beale's publication of one of Greco's manuscript texts offers a provocative definition of the term.
[A] Gambett signifies here a game, so contrived, that he which loseth shall have a palpable reason for every remove he maketh, whereas the reasons of the removes of the winner are so hard to be found out, that they seem rather preposterous, and unfitting, which sheweth the excellent contrivance and invention of the Authors of them.
The Royall Game of Chesse-Play (London, 1656), frontmatter.