intrusive adj.

late 14c., "unjust invasion of property or usurpation of office," from Old French intrusion (14c.), from Medieval Latin intrusionem (nominative intrusio) "a thrusting in," noun of action from past participle stem of Latin intrudere "to thrust in, force in," from in- "in" (from PIE root *en "in") + trudere "to thrust, push," from PIE *treud- "to press, push, squeeze" (see threat).

Meaning "a thrusting or pushing in" is from 1590s; that of "act of intruding" is from 1630s. Geological sense is from 1816.

word-forming element making adjectives from verbs, meaning "pertaining to, tending to; doing, serving to do," in some cases from Old French -if, but usually directly from Latin adjectival suffix -ivus (source also of Italian and Spanish -ivo). In some words borrowed from French at an early date it has been reduced to -y (as in hasty, tardy).