The phrase 'not the sharpest knife in the drawer' is a colloquial expression used to describe someone who is not particularly intelligent. The crossword solutions for this phrase are MUTTONHEAD (10 letters), IDIOT (5 letters), OBTUSE (6 letters), and DIM (3 letters). MUTTONHEAD is a slang term for a foolish or stupid person, while IDIOT is a more direct insult for someone who is not very bright. OBTUSE is an adjective meaning not having a sharp point or angle, which is a metaphor for someone who is not quick-witted. Finally, DIM is another adjective meaning lacking brightness or intelligence. All of these words can be used to describe someone who is not the sharpest knife in the drawer.