One who or that which checks or verifies something.
So, keep in mind that Microsoft Word’s Spelling tool is as much a “typo” tool as a checker of spelling.1992, Neil J. Salkind, Applying Macintosh: Solutions, Ideas, and Tools, Macmillan Publishing Company, →ISBN, page 205:
2
One who makes a check mark.
"Essentially," said a senior vice president of the FHLBB of Dallas, "we were checkers of boxes."1989, M. Manfred Fabritius, William Borges, Saving the Savings and Loan:
3
The clerk who tallies cost of purchases and accepts payment.
There was a long line at the grocery store because the checker was so slow.
Bud Brown said something to the checker he was supervising; she had been craning around to see what was happening. She flushed and began to run her calculator again.1980, Stephen King, The Mist, Viking Press:
Etymology From Middle English cheker, aphetic from Anglo-Norman escheker (“chessboard”), from Latin scaccarium, thus ultimately morpheme-for-morpheme cognate to etymology 1.
1
To mark in a pattern of alternating light and dark positions, like a checkerboard.
On the other hand, who ever tires of the names of Oldfield, and Bracegirdle, and Woffington? All the flutters of the fans of two centuries, and all the solid merits of bodices and petticoats, come down to us in their names; chequering Covent Garden like chintz, and bringing along with them the periwigged and scented glories of the Congreves and Steeles.1847, Leight Hunt, Men, Women and Books a Selection of Sketches, Essays, and Critical Memoirs from His Uncollected Prose Writing by Leigh Hunt, page 288:
2
To develop markings in a pattern of alternating light and dark positions, like a checkerboard.
checker
noun
Etymology From Middle English cheker, aphetic from Anglo-Norman escheker (“chessboard”), from Latin scaccarium, thus ultimately morpheme-for-morpheme cognate to etymology 1.
1
A playing piece in the game of checkers (British: draughts), or certain other table games such as backgammon.
2
A pattern of alternating colours as on a chessboard.