Recruit (6)
'recruit' is the definition.
(I know that recruit is a more specific form of enlist)
This is all the clue.
(Other definitions for enlist that I've seen before include "Join the armed services" , "Draft" , "Engage" , "Sign on -- 13 (anag)" , "Take the Queen's shilling" .)
(Other definitions for rookie that I've seen before include "untrained soldier" , "inexperienced fighter" , "New (police) recruit (colloq.)" , "untested type" , "new team member" .)
'recruit' is the definition.
(thesaurus)
This is all the clue.
(Other definitions for hire that I've seen before include "Pay to use something" , "Rent, employ" , "Pay for temporary use" , "Rent or lease" , "Engage (taxi)" .)
(Other definitions for tap that I've seen before include "indicate availability" , "Light touch (hot or cold?)" , "water supply" , "It's called a faucet in America" , "Flow controller; knock" .)