Etymology
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perspire (v.)

1640s, of a volatile liquid, "to evaporate through the pores" (intransitive), a back-formation from perspiration and in part from Latin perspirare "blow or breathe constantly," from per "through" (from PIE root *per- (1) "forward," hence "through") + spirare "to breathe, blow" (see spirit (n.)). The meaning "to sweat, to give out watery substance through the pores of the skin" (intransitive) is a polite usage attested from 1725. Medical men tried to maintain a distinction between "sensible" (sweat) and "insensible" perspiration:

[I]t is sufficient for common use to observe, that perspiration is that insensible discharge of vapour from the whole surface of the body and the lungs which is constantly going on in a healthy state; that it is always natural and always salutary; that sweat, on the contrary, is an evacuation, which never appears without some uncommon effort, or some disease to the system, that it weakens and relaxes, and is so far from coinciding with perspiration, that it obstructs and checks it. [Charles White, "A Treatise on the Management of Pregnant and Lying-in Women," London, 1791]

Related: Perspired; perspiring.

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anti-perspirant (adj.)

also antiperspirant, 1935, in advertisements for Nonspi ("The Safe Anti-Perspirant for Fastidious Women"), from anti- + perspire, probably modeled on older deodorant. Technically an application preventing or restricting the flow of perspiration, as opposed to a deodorant, which deodorizes only and in no way affects secretion.

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*per- (1)

Proto-Indo-European root forming prepositions, etc., meaning "forward," and, by extension, "in front of, before, first, chief, toward, near, against," etc.

It forms all or part of: afford; approach; appropriate; approve; approximate; barbican; before; deprive; expropriate; far; first; for; for-; fore; fore-; forefather; foremost; former (adj.); forth; frame; frau; fret; Freya; fro; froward; from; furnish; furniture; further; galore; hysteron-proteron; impervious; improbity; impromptu; improve; palfrey; par (prep.); para- (1) "alongside, beyond; altered; contrary; irregular, abnormal;" paradise; pardon; paramount; paramour; parvenu; pellucid; per; per-; percent; percussion; perennial; perestroika; perfect; perfidy; perform; perfume; perfunctory; perhaps; peri-; perish; perjury; permanent; permeate; permit; pernicious; perpendicular; perpetual; perplex; persecute; persevere; perspective; perspire; persuasion; pertain; peruse; pervade; pervert; pierce; portray; postprandial; prae-; Prakrit; pre-; premier; presbyter; Presbyterian; preterite; pride; priest; primal; primary; primate; primavera; prime; primeval; primitive; primo; primogenitor; primogeniture; primordial; primus; prince; principal; principle; prior; pristine; private; privilege; privy; pro (n.2) "a consideration or argument in favor;" pro-; probably; probe; probity; problem; proceed; proclaim; prodigal; produce; profane; profess; profile; profit; profound; profuse; project; promise; prompt; prone; proof; proper; property; propinquity; prophet; prose; prostate; prosthesis; protagonist; Protean; protect; protein; Proterozoic; protest; proto-; protocol; proton; protoplasm; Protozoa; proud; prove; proverb; provide; provoke; prow; prowess; proximate; Purana; purchase; purdah; reciprocal; rapprochement; reproach; reprove; veneer.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit pari "around, about, through," parah "farther, remote, ulterior," pura "formerly, before," pra- "before, forward, forth;" Avestan pairi- "around," paro "before;" Hittite para "outside of," Greek peri "around, about, near, beyond," pera "across, beyond," paros "before," para "from beside, beyond," pro "before;" Latin pro "before, for, on behalf of, instead of," porro "forward," prae "before," per "through;" Old Church Slavonic pra-dedu "great-grandfather;" Russian pere- "through;" Lithuanian per "through;" Old Irish ire "farther," roar "enough;" Gothic faura "before," Old English fore (prep.) "before, in front of," (adv.) "before, previously," fram "forward, from," feor "to a great distance, long ago;" German vor "before, in front of;" Old Irish air- Gothic fair-, German ver-, Old English fer-, intensive prefixes.

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perspiration (n.)

1610s, "a breathing through," a sense now obsolete, from French perspiration (1560s), noun of action from perspirer "perspire," from Latin perspirare "blow or breathe constantly," from per "through" (from PIE root *per- (1) "forward," hence "through") + spirare "to breathe, blow" (see spirit (n.)). Applied by 1620s to "excretion of invisible moistures through the skin," hence its later use as a euphemism for "sweat" (1725).

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sweat (v.)

Old English swætan "perspire," also "work hard," from Proto-Germanic *swaitjan "to sweat," from the source of sweat (n.). Compare Frisian swette, Dutch zweeten, Danish svede, German schwitzen. Meaning "to be worried, vexed" is recorded from c. 1400. Transitive sense is from late 14c. Related: Sweated; sweating. Sweating sickness was a sudden, often-fatal fever, accompanied by intense sweating, that struck England 1485 and returned periodically through mid-16c., described in the original citation (a chronicle from 1502) as "a grete deth and hasty."

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