1660s, kind of tights-like garment for men (consisting of breeches and stockings in one; originally a French fashion and execrated as such by late 17c. English writers), associated with Pantaloun,Pantaloon (1580s), the silly old man character in Italian comedy, who wore spectacles, slippers, and tight trousers over his skinny legs.
His name is from Italian Pantalone, from San Pantaleone, a Christian martyr who was a popular saint in Venice (Pantaloon in the comedies represents the Venetian). The name, a favorite one among the Venetians, is of Greek origin and means "all-compassionate" (Littré), or, according to Klein, Century Dictionary, etc., "entirely lion," perhaps in reference to the lion symbolic of St. Mark.
By 1798 the word was revived in reference to tight long trousers buttoned or tied below the knee (replacing knee-breeches), worn by men of fashion. These were gradually replaced by modern trousers, but the name persisted. Pants is a shortened form attested by 1840. The diminutive pantalettes for "loose drawers with frills at the bottoms of the legs, worn by young girls," is by 1834.