Closely compacted (5)
I believe the answer is:
dense
'closely compacted' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for dense that I've seen before include "Closely-spaced" , "Not very bright" , "Close - compact - stupid" , "Needs (anag) -- thick" , "Stupid; compacted" .)