Sandbank about to return and drift sideways (4)
I believe the answer is:
crab
'drift sideways' is the definition.
(to move like a crab)
'sandbank about to return' is the wordplay.
'sandbank' becomes 'bar' (I've seen this before).
'about' becomes 'c' (abbreviation for 'circa').
'to return' is a reversal indicator.
'bar'+'c'='barc'
'barc' backwards is 'CRAB'.
'and' is the link.
(Other definitions for crab that I've seen before include "Sourpuss < to wreck" , "Marine crustacean (seen on 1 across?)" , "Edible crustacean" , "One fired from gun" , "A crustacean; type of apple" .)