spot check
noun phrase

- an inspection or investigation that is carried out at random or limited to a few instances

American Heritage Dictionary

- a quick examination of a few members of a group instead of the whole group

Cambridge Advanced Learner's Dictionary

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Spot check stems from the sense of spot as in "a place or a position." Thus the idea of a spot check is to inspect something only in certain "spots" instead of the whole or everything, particularly when a comprehensive check would be impractical or impossible.

The word spot can be traced back to the 12th century and the Old English "splott," meaning a mark on the surface of something or a patch of land/piece of ground. Spot was likely influenced by the Middle Dutch "spotte," which has the same sense.

Most of the Frisian dialects used the word "spot" in a similar context, such as in a "speck" of something, a speck being a small spot or stain (not to be confused with the German word for bacon, "Speck").

Even more interesting is the etymology of "check", a 14th century word that originally (and still) refers to an action in the game of chess when a move has exposed the opponent's king. This was borrowed from the Old French "eschec/ashac," which stems from the Arabic and Persian "shah." Out of this usage in chess, check then evolved to mean, among many other things, an action or influence that stops motion or expression.

Source: Barnhart Dictionary of Etymology

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SYNONYMS

random investigation, random sampling, surprise inspection, sudden check, on-the-spot check

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Practice OWAD in a conversation:

"Be sure to buy a ticket when riding German subways because you might be subjected to a SPOT CHECK."