【Insipid】 , 【vapid】 ,  【flat】 ,  【jejune】 ,  【banal】 ,  【wishy-washy】 ,  【inane】  mean devoid of qualities which give spirit, character, or substance to a thing.

Something  【insipid】 is without taste, or savor, or pungency; the term is applied not only to food and drink which are so tasteless as to give no pleasure or stimulation to the palate, but also to persons and their utterances and ideas which strike one as thin, weak, and characterless and leave one completely indifferent.

Something  【vapid】 is stale, uninteresting, or pointless because it has lost its characteristic taste, freshness, spirit, sparkle, or tang.

Something  【flat】 is so 【vapid】 that it seems dead or lifeless. The word is applied chiefly to what has lost all savor, sparkle, zest, or capacity for stimulating interest or pleasure.

Something  【jejune】 is so devoid of substance or nutritive quality that it cannot satisfy the appetite; the word is only occasionally used with reference to physical hunger and is usually employed with reference to hunger of the mind or the emotions. It often connotes barrenness, aridity, or meagerness in addition to its basic implications.

Something  【banal】 is so commonplace or so trite that it lacks all freshness or power to stimulate or appeal. The term often also carries one or more of such various connotations as tastelessness, pedestrianism, triviality, or platitudinousness.

Something  【wishy-washy】 has the essential or characteristic qualities so weak or diluted that it strikes one as extremely 【insipid】 or 【vapid】 .

Something  【inane】 is devoid of sense, significance, or point.