friable adj.

1560s, "a chafing, rubbing," from French friction (16c.) and directly from Latin frictionem (nominative frictio) "a rubbing, rubbing down," noun of action from past-participle stem of fricare "to rub, rub down," which is of uncertain origin. Watkins suggests possibly from PIE root *bhreie- "to rub, break." De Vaan suggests a PIE bhriH-o- "to cut" and compares Sanskrit bhrinanti, Old Church Slavonic briti "to shave." Sense of "resistance to motion" is from 1722; figurative sense of "disagreement, clash, lack of harmony, mutual irritation" first recorded 1761. Related: Frictional.

mid-15c., from Latin frivolus "silly, empty, trifling, worthless," diminutive of *frivos "broken, crumbled," from friare "break, rub away, crumble" (see friable). In law (by 1736), "so clearly insufficient as to need no argument to show its weakness." Related: Frivolously; frivolousness.