Related Clues:

• None too swift
• Hardly suited for Mensa
• Slow to understand
• Not the brightest bulb on the Christmas tree
• Sold-out show
• Thickly populated
• Bubbleheaded
• Thickly packed
• Heavy, as fog
• Rearranged needs?
• Solid
• Thick-headed
• Very thick
• Close-knit
• Jam-packed