Sire/ˈsaɪər/ Definition 1 of 4Pro Tip 1/2Animal Lineage Use 'sire' to discuss an animal's male lineage, commonly with pedigree animals. The pedigree certificate listed the puppy's sire. Pro Tip 2/2Breeding Context 'Sire' is often used in the context of animal breeding and genetics. The breeder kept detailed records of each mare and her sire.