1.To fuck.
Originating from the horse breeding industry where "service" is a euphemism for bringing the stud to mount the mare. Same as tupping in
sheep breeding.
2. To have sex with a mardy bitch to keep her
happy, as in a mechanic servicing a car to keep it
running smoothly.
From the 'The Talented Mr Ripley':
Dick Greenleaf (Jude Law) on a
boat trip: "Marge needs a service" - winks at his mates and proceeds below
deck and give his sulky
bird a good seeing to.