Those above, go west using tiller in swamp? (9)
I believe the answer is:
overwhelm
'swamp?' is the definition.
(I've seen this before)
'those above go west using tiller' is the wordplay.
I cannot quite see how this works, but
'above' could be 'over' (I've seen this before) and 'over' is present in the answer.
'west' could be 'w' (abbreviation) and 'w' is present in the answer.
'tiller' could be 'helm' (I've seen this in another clue) and 'helm' is present in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
'in' is the link.
Can you help me to learn more?
(Other definitions for overwhelm that I've seen before include "Snow under" , "Swamp - have a strong emotional effect on" , "Completely defeat" , "Vanquish" , "Conquer" .)