adjective

causing or resulting in a feeling of miserable dejection.

that thought is too depressing for words

upsetting,distressing,painful,heartbreaking,heart-rending,dispiriting,disheartening,discouraging,demoralizing,dismal,bleak,black,sombre,gloomy,grave,unhappy,melancholy,sad,saddening,wretched,doleful,daunting,disenchanting,unfavourable,morbid,blue,dejecting,distressful,lachrymose,dreary,grim,drab,dark,dingy,funereal,miserable,cheerless,joyless,comfortless,uninviting,drear