LUSCIOUS

The word “luscious” typically means having a pleasingly rich, sweet, or appetizing flavour. Therefore, the word that is opposite in meaning to “luscious” would be: Option B) insipid.

 “Insipid” means lacking flavour or taste; unappetizing. 

Option A: “Fickle” means changing frequently, especially regarding one’s loyalties or affections.

Option C: “Languid” means slow and relaxed or weak or faint from illness or fatigue.

Option D: “Deteriorating” means becoming progressively worse.

Therefore, “insipid” is the most appropriate choice here as it is the opposite of the meaning of “luscious”.