verb tr., intr.: To perceive, without counting, the number of objects in a small group.
From Latin subitus (sudden), from past participle of subire (to appear suddenly), from sub- (under) + ire (to go). Earliest documented use: 1949.
“Brian Butterworth’s explanation focuses on our uncanny ability to subitise. Up to four or five objects, most people can tell how many there are just by looking, without counting each one. But if there are more objects, we have to count.”
Emily Sohn; Number of the Beasts; New Scientist (London, UK); Jan 24, 2004.
“Getting the computer model to subitize the way humans and animals did was possible, Stanislas Dehaene found, only if he built in ‘number neurons’.”
Jim Holt; Numbers Guy; New Yorker; Mar 3, 2008.