I'm taken aback about swamp (4)
I believe the answer is:
mire
'swamp' is the definition.
(thesaurus)
'i'm taken aback about' is the wordplay.
'taken aback' says the letters should be written backwards.
'about' becomes 're' (regarding**).
'im' in reverse letter order is 'mi'.
'mi'+'re'='MIRE'
(Other definitions for mire that I've seen before include "Bog down in swamp" , "(Stretch of) clinging mud" , "Soft mud or dirt" , "Bog - muck" , "Stretch of boggy ground" .)