Delayed having most of the milky sap (4)
I believe the answer is:
late
'delayed' is the definition.
(I've seen this in other clues)
'most of the milky sap' is the wordplay.
'most of' means to remove the last letter.
'the milky sap' becomes 'latex' (I've seen this before).
'latex' with its last letter taken off is 'LATE'.
'having' acts as a link.
(Other definitions for late that I've seen before include "Passed on (but still not passed by!)" , "Delayed; dead" , "Yet to arrive?" , "not quick enough" , "No longer alive; tardy" .)