Sail's support (4)
(Other definitions for mast that I've seen before include "Acorns, etc., fed to pigs" , "nuts and seeds" , "Television transmitter" , "Pole on ship" , "Spar to support a sail" .)
'sail's support' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for spar that I've seen before include "Translucent mineral" , "dispute" , "quarrel" , "microcrystalline mineral?" , "Act as boxer" .)