Conceited

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late Middle English (in the sense ‘notion’, also ‘quaintly decorative article’): from conceive, on the pattern of pairs such as deceive, deceit .

wiktionary

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conceit +‎  -ed

See conceit(verb)

etymonline

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conceited (adj.)

c. 1600, "having an overweening opinion of oneself" (short for self-conceited, 1590s), past-participle adjective from conceit (v.) "conceive, imagine, think" (1550s), a now-obsolete verb from conceit (n.). Earlier it meant "having intelligence, ingenious, witty" (1540s). Related: Conceitedly; conceitedness.