early 15c., "to scatter, disperse (as the wind does)," from Latin ventilatus, past participle of ventilare "to brandish, toss in the air, winnow, fan, agitate, set in motion," from ventulus "a breeze," diminutive of ventus "wind" (from PIE *wē-nt-o‑ "blowing," suffixed (participial) form of root *we- "to blow").
Original notion is of cleaning grain by tossing it in the air and letting the wind blow away the chaff. Meaning "supply a room with fresh air" first recorded 1743, a verbal derivative of ventilation. Formerly with diverse slang senses, including "shoot" (someone), recorded from 1875, on the notion of "make holes in." Related: Ventilated; ventilating.
"club-shaped instrument used for pounding and breaking materials in a mortar," mid-14c. pestel, (as a surname late 13c.), from Old French pestel and directly from Latin pistillum (Medieval Latin pestellum) "pounder, pestle," related to pinsere "to pound," from PIE *pis-to-, suffixed form of root *peis- "to crush" (source also of Sanskrit pinasti "pounds, crushes," pistah "anything ground, meal," Greek ptissein "to winnow," Old Church Slavonic pišo, pichati "to push, thrust, strike," pišenica "wheat," Russian pseno "millet").
Also in old use "the leg of certain animals used for food" (14c.), hence pestle of a lark "a trifle, an unimportant matter" (1590s).