It's dreadful in the crowd - I retreated (4)
I believe the answer is:
dire
'it's dreadful' is the definition.
(synonyms)
'in the crowd i retreated' is the wordplay.
'in' indicates a hidden word.
'DIRE' is hidden in the letters of 'crowd i retreated'.
(Other definitions for dire that I've seen before include "Desperate; dreadful" , "Extremely serious or urgent" , "Really dreadful - ride on" , "Very serious indeed" , "Disastrous" .)