Definition: "study of roots"

This is an anagram - look for an indicator word that suggests mixing or rearranging letters

'Exciting' is the anagram indicator - rearrange the letters of 'YET GLOOMY' to form the answer

Answer: ETYMOLOGY | 'Exciting' indicates anagram - rearrange the letters of 'YET GLOOMY' = ETYMOLOGY (study of word origins/roots)