Crow's-nest support (4)
I believe the answer is:
mast
'crow's-nest support' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for mast that I've seen before include "Pole aboard; fruit for pigs" , "nuts and seeds" , "it rises on board a ship" , "Television transmitter" , "Vertical spar for supporting sails etc" .)