The Alaunt is more a type of dog rather than a breed its self.
Scotsman has already said this. Alaunt is the old name used for mastiff type dogs.
It must be kept in mind that Alaunts were not a breed;Phoebus describes three principal types:
one resembling a strong-headed greyhound,anouther a powerful hunting mastiff of great dane construction and a third a short faced butchers dog or catch-dog,the ancestorof the baiting dog.
Quoted from The running mastiffs by colonel David hancock.
Well worth a read to any dog man.