WordWeb Online

1. Making a strong or vivid impression
   "an impressive ceremony"
    
2. Producing a strong effect
   "gave an impressive performance as Othello";
   - telling

See also: amazing, arresting, astonishing, astounding, awe-inspiring, awesome, awful [archaic], awing, baronial, brilliant, dazzling, dramatic, effective, effectual, efficacious, expansive, eye-popping, formidable, fulgurant, fulgurous, gallant, glorious, grand, grandiose, heroic, important-looking, imposing, lofty, magnificent, majestic, mind-boggling, moving, noble, palatial, proud, sensational, signal, spectacular, splendid, staggering, stately, striking, stunning, stupefying, thundering

Antonym: unimpressive

Encyclopedia: Impressive