criterion

—Can be confused: 1. criteria, criterion (see usage note at criterion); 2. criteria, criterion (see usage note at this entry).

—Synonyms
measure, touchstone, yardstick. See standard.

—Usage note
Like some other nouns borrowed from the Greek, criterion has both a Greek plural, criteria, and a plural formed on the English pattern, criterions. The plural in -a occurs with far greater frequency than does the -s plural: These are the criteria for the selection of candidates. Although criteria is sometimes used as a singular, most often in speech and rather infrequently in edited prose, it continues strongly in use as a plural in standard English, with criterion as the singular.