Dejected crowd initially remain totally stuck in Slough (11)
I believe the answer is:
crestfallen
'dejected' is the definition.
(similar in meaning)
'crowd initially remain totally stuck in slough' is the wordplay.
'initially' indicates taking the first letters.
'remain' becomes 'rest' (synonyms).
'totally stuck in slough' becomes 'fallen' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
The first letter of 'crowd' is 'c'.
'c'+'rest'+'fallen'='CRESTFALLEN'
Can you help me to learn more?
(Other definitions for crestfallen that I've seen before include "Deflated" , "Downcast" , "Dejected after a failure" , "Low" , "Sadly disappointed" .)