c. 1400, exale, transitive, originally of liquids, perfumes, the breath of life, etc., from Old French exhaler (14c.) and directly from Latin exhalare "breathe out, evaporate," from ex "out" (see ex-) + halare "breathe." Of living things, "to breathe out," 1580s transitive; by 1837 intransitive. Related: Exhaled; exhaling.
late 14c., "act of exhalation; that which is exhaled," from Latin exhalationem (nominative exhalatio) "an exhalation, vapor," noun of action from past-participle stem of exhalare "to breathe out" (see exhale).
c. 1400, "to die," from Old French expirer "expire, elapse" (12c.), from Latin expirare/exspirare "breathe out, blow out, exhale; breathe one's last, die," hence, figuratively, "expire, come to an end, cease," from ex "out" (see ex-) + spirare "to breathe" (see spirit (n.)). "Die" is the older sense in English; that of "breathe out" is attested from 1580s. Of laws, patents, treaties, etc., mid-15c. In 17c. also transitive. Related: Expired; expiring.
"to draw air into and expel it from the lungs; to inhale and exhale (a scent, etc.)," c. 1200, not in Old English, but it retains the original Old English vowel of its source word, breath. To breathe (one's) last "die" is from 1590s. To breathe down the back of (someone's) neck "be close behind" is by 1946. Related: Breathed; breathing.