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early 15c., "vapor, breath," from Middle French expiration, from Latin expirationem/exspirationem (nominative expiratio/exspiratio), noun of action from past participle stem of expirare/exspirare (see expire). Meaning "termination, end, close" is from 1560s.
expiration ex·pi·ra·tion (ěk'spə-rā'shən)