"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), with -phobia "fear" + Latin claustrum "a bolt, a means of closing; a place shut in, confined place, frontier fortress" (in Medieval Latin "cloister"), from past participle of claudere "to close" (see close (v.)).
