Leave with valetudinarian (4)
I believe the answer is:
will
'leave' is the definition.
(I know that leave can be written as will)
'with valetudinarian' is the wordplay.
'with' becomes 'w' (abbreviation).
'valetudinarian' becomes 'ill' (I've seen this before).
'w'+'ill'='WILL'
(Other definitions for will that I've seen before include "Volition" , "Intend; document" , "Fixed intention" , "Final disposition" , "A traditional question from the floor?" .)