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"morbid fear of being shut up in a confined space," coined 1879 (in article by Italian-born, French-naturalized Swiss-English physician Dr. Benjamin Ball (1834-1892)) from Latin claustrum "a bolt, a means of closing; a place shut in, confined place, frontier fortress" (in Medieval Latin "cloister"), past participle of claudere "to close" (see close (v.)) + -phobia "fear."
claustrophobia claus·tro·pho·bi·a (klô'strə-fō'bē-ə)
An abnormal fear of being in narrow or enclosed spaces.
An abnormal fear of being shut in or enclosed.