The term 'lacking depth' can be described by the crossword solutions TWOD (4 letters), SHALLOW (7 letters), ONED (4 letters), and FACILE (6 letters). TWOD stands for two-dimensional, which means having only two dimensions, such as length and width. SHALLOW is defined as not deep or having little substance. ONED is a reference to one-dimensional, which is similar to two-dimensional but with only one dimension, such as length. Finally, FACILE is an adjective meaning easy or superficial. Together, these words describe something that is lacking in depth, complexity, or substance.