Crooked old partner has absconded to the borders (6)
I believe the answer is:
flexed
'crooked' is the definition.
(I've seen this before)
'old partner has absconded to the borders' is the wordplay.
'old partner has' becomes 'xe' (I can't explain this - if you can you should give a lot more credence to this answer).
'absconded' becomes 'fled' (I've seen this in another clue).
'to the borders' means one lot of letters goes inside another (inserted letters are bordered by others).
'xe' put inside 'fled' is 'FLEXED'.
Can you help me to learn more?
(Other definitions for flexed that I've seen before include "Crooked" , "Bent, warped" , "Bent (muscles)" , "Tightened a muscle" .)