A whoremaster can refer to a pimp or a man who prefers to shag women of easy virtue (e.g. tarts/ prostitutes)
"That guy will shag anything man. He's a right fuckin whoremaster"
"Take yer bags and fuck off out of my house, ya whoremasterin' bastard!"
"A man who will shag absulutly anyone, anytime"
"You shagged them 3 girls in 2 days?" Your a whoremaster.
"You shagged that 60 year old granny with the beard?" Your a whoremaster"