Related Clues:

• Compressed - obtuse
• Tightly packed - stupid
• Close - compact - stupid
• Close together
• Needs (anag)
• Not so swift on the uptake
• Not getting it
• Like dunderheads
• Like a copse
• Thick — compact
• Like pea-soup fog
• Ends badly for sweetheart in tight crowd
• Not at all sharp
• Like some populations
• Scarcely bright