Excavate channel backwards, being pompous (6)
I believe the answer is:
turgid
'pompous' is the definition.
(I've seen this before)
'excavate channel backwards' is the wordplay.
'excavate' becomes 'dig' (synonyms).
'channel' becomes 'rut' (I've seen this in another clue).
'backwards' is a reversal indicator.
'dig'+'rut'='digrut'
'digrut' backwards is 'TURGID'.
'being' acts as a link.
(Other definitions for turgid that I've seen before include "Enlarged" , "Swollen; bombastic" , "Swollen and distended" , "Pompously inflated" , "(Of style) bombastic" .)