Antonyms of adj light-hearted

1 sense of light-hearted

Sense 1
blithe, blithesome, lighthearted, lightsome, light-hearted -- (carefree and happy and lighthearted; "was loved for her blithe spirit"; "a merry blithesome nature"; "her lighthearted nature"; "trilling songs with a lightsome heart")

INDIRECT (VIA cheerful) -> depressing, cheerless, uncheerful -- (causing sad feelings of gloom and inadequacy; "the economic outlook is depressing"; "something cheerless about the room"; "a moody and uncheerful person"; "an uncheerful place")
                                                                         

Similarity of adj light-hearted

1 sense of light-hearted

Sense 1
blithe, blithesome, lighthearted, lightsome, light-hearted -- (carefree and happy and lighthearted; "was loved for her blithe spirit"; "a merry blithesome nature"; "her lighthearted nature"; "trilling songs with a lightsome heart")
       => cheerful (vs. depressing) -- (being full of or promoting cheer; having or showing good spirits; "her cheerful nature"; "a cheerful greeting"; "a cheerful room"; "as cheerful as anyone confined to a hospital bed could be")