Wader's granny? (4)
I believe the answer is:
knot
This clue is a double definition.
'wader's' is the first definition.
(type of wading bird)
'granny?' is the second definition.
(granny is a kind of knot)
(Other definitions for knot that I've seen before include "See 2" , "A sheepshank or bowline" , "To secure < > bird" , "It may be tied" , "Unit of length used in navigation" .)