google
ref
late 19th century: modern Latin, from Latin claustrum ‘lock, bolt’ + -phobia.
wiktionary
ref
claustrophobia + -ic
etymonline
ref
claustrophobic (adj.)
"affected by claustrophobia," 1889, from claustrophobia + -ic. As a noun, "person who has claustrophobia," it is recorded from 1953.
