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1610s, from French perspiration (1560s), noun of action from perspirer "perspire," from Latin perspirare "blow or breathe constantly," from per- "through" (see per) + spirare "to breathe, blow" (see spirit (n.)). Applied to excretion of invisible moistures through the skin (1620s), hence used as a euphemism for "sweat" from 1725.
perspiration per·spi·ra·tion (pûr'spə-rā'shən)
The fluid, consisting of water with small amounts of urea and salts, that is excreted through the pores of the skin by the sweat glands.
The act or process of excreting this fluid through the pores of the skin.