Definition of sad :
1. Affected with grief or unhappiness; cast down with affliction; downcast; gloomy; mournful.
2. Afflictive; calamitous; causing sorrow; as, a sad accident; a sad misfortune.
3. Dull; grave; dark; somber; - said of colors.
4. Heavy; weighty; ponderous; close; hard.
5. Hence, bad; naughty; troublesome; wicked.
6. Sated; satisfied; weary; tired.
7. Serious; grave; sober; steadfast; not light or frivolous.
8. To make sorrowful; to sadden.
happy, cast down, no-good, perturbing, deplorable, distressing, saddening, good-for-nothing, hopeless, brokenhearted, bittersweet, regretful, no-account, regrettable, mourning, distressful, dull, tragicomic, grievous, good-for-naught, no-count, dismal, tragic, gay, vicious, spiritless, cut up, yearning, down, tristful, execrable, careworn, poor, downcast, forlorn, pitiable, unhappy, dark, heavy, afflicted, drab, wretched, morbid, melancholic, lamenting, bitter, meritless, oppressive, distressed, unfortunate, condemnable, tragicomical, cheerless, horrified, weeping, dispiriting, somber, touching, crestfallen, troubling, funereal, doleful, worrying, reprehensible, jaundiced, pitiful, depressive, oppressed, drear, rueful, worrisome, hapless, saturnine, heavy-hearted, moving, lugubrious, misfortunate, heavyhearted, disquieting, apprehensive, dysphoric, worried, desolate, dire, languishing, troubled, discouraging, foreboding, criminal, piteous, low, pessimistic, pathetic, sorrowful, disturbing, sorry, tragical, lamentable, dingy, poignant, bad, woebegone, heart-rending, depressing
dejected (part of speech: adjective)
contemplative, discouraged, disconsolate, grim, dejected, anxious, downhearted, woeful, heartbroken, gloomy, lachrymose, sullen, despondent, dreary, depressed, disheartened, mournful, glum, morose, despairing, miserable, anguished, joyless, moody, pensive, wistful, plaintive, blue, melancholy, overcome, dispirited, dolorous
inferior (part of speech: noun)