checker

noun

1. 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.”

2. One who makes a check mark.

   “"Essentially," said a senior vice president of the FHLBB of Dallas, "we were checkers of boxes."”

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.”

4. One who hinders or stops something.
5. A playing piece in the game of checkers (British: draughts), or certain other table games such as backgammon.
6. A pattern of alternating colours as on a chessboard.
7. An individual square appearing in such a pattern.
8. The fruit of the wild service tree or chequer tree, Photinia villosa, syn. Sorbus terminalis

verb

1. (transitive)To mark in a pattern of alternating light and dark positions, like a checkerboard.
2. (intransitive)To develop markings in a pattern of alternating light and dark positions, like a checkerboard.