impassable, a. [impenetrable], [pathless], [impervious].
impatient, a. [restless], [restive], [fretful], eager, impetuous.
impede, v. [retard].
impediment, n. [obstacle], [barrier], [obstruction], stumblingblock.
impending, a. imminent, [threatening].
impenetrable, a. [impervious], imperforable.
impenitence, n. incontrition, obduracy, impenitency.
impenitent, a. incontrite, [unrepentant], obdurate, incorrigible, recusant, [relentless].
imperative, a. [binding], [compulsory], [obligatory], [imperious], peremptory.
imperfect, a. defective, [faulty], [deficient], [undeveloped], [abortive], [fallible], [frail], errable.