The term 'lacking substance' can be described by the following crossword solutions: TENUOUS (7 letters), THIN (4 letters), FLIMSY (6 letters), AIRY (4 letters), INANE (5 letters), and Innominate (10 letters). All of these words refer to something that is not solid or substantial, and can be used to describe a lack of depth or meaning. TENUOUS refers to something that is weak or fragile, THIN implies something that is not thick or dense, FLIMSY suggests something that is easily broken or destroyed, AIRY implies something that is light or unsubstantial, INANE means something that is silly or foolish, and Innominate implies something that is without name or identity.