Cancel boat to collect the King (5)
I believe the answer is:
scrub
'cancel' is the definition.
(scrub can mean to cancel or erase)
'boat to collect the king' is the wordplay.
'boat' becomes 'sub' (submarine).
'to collect' indicates putting letters inside (inserted letters are collected by others).
'the king' becomes 'CR' (short for Carolus Rex, King Charles in Latin).
'sub' enclosing 'cr' is 'SCRUB'.
(Other definitions for scrub that I've seen before include "Area of dense stunted vegetation" , "Axe" , "something in the garden?" , "stunted trees and brushwood" , "Clean, low vegetation" .)