cinch

Etymology 1

Borrowed from Occitan cencha, from Latin cincta, or from Spanish cincha (“a belt or girth”), from Late Latin cingula, from Latin cingulum. Doublet of cingle.

noun

1. A simple saddle girth used in Mexico.
   He found Andy morosely replacing some broken strands in his cinch, and he went straight at the mooted question. 1915, B. M. Bower, The Flying U's Last Stand
2. (informal) Something that is very easy to do.
   We thought we had a cinch on getting out by way of this cord and so we followed that. 1913, Major Archibald Lee Fletcher, Boy Scouts in the Coal Caverns
   The job was a snap. I travelled the country averaging a thousand miles a week and, since the previous incumbent had been a lazy bugger, managed to treble the business. It was a cinch. 2003, Clive Selwood, All the Moves (but None of the Licks), page 33
3. (informal) Something that is obvious or certain to occur; a sure thing.
   As a matter of fact, from the look of Elmer's shoulder, it wasn't a cinch that he would ever pitch again. 11 March 1916, Charles E. Van Loan, “His Folks”, in Saturday Evening Post
4. (informal) A firm hold.
   You've got the cinch on him. You could send him to quod, and I'd send him there as quick as lightning. I'd hang him, if I could, for what he done to Lil Sarnia. 1916, Gilbert Parker, The World For Sale,

verb

1. To bring to certain conclusion.
2. To tighten down.
   [Ostriches] also lack the tiny hooks, or barbicels, that cinch feathers together in most other birds. August 4, 2020, Richard Conniff, “They may look goofy, but ostriches are nobody’s fool”, in National Geographic Magazine

Etymology 2

Compare senses at etymology 1 (a girth, a tight grip), perhaps suggesting the tactics used in the game; or perhaps from Spanish cinco (“five”), the five spots of the colour of the trump being important cards.

noun

1. (card games) A variety of auction pitch in which a draw to improve the hand is added, and the five of trumps (called "right Pedro") and the five of the same colour (called "left Pedro", and ranking between the five and the four of trumps) are each worth five. Fifty-one points make a game.

verb

1. (card games) In the game of cinch, to protect (a trick) by playing a higher trump than the five.