imposing, a. impressive, [stately], [majestic], [august].
impossibility, n. [impracticability].
impossible, a. [impracticable], unfeasible, [unattainable].
impostor, n. pretender, [cheat], [charlatan], [mountebank], [quack], [deceiver].
imposture, n. [fraud], imposition, charlatanism, [deception].
impracticability, n. unfeasibility.
impracticable, a. [impossible], unfeasible.
impregnate, v. fecundate.
impregnation, n. fecundation.
imprison, v. incarcerate, immure.