1) Altering 2) Castration 3) Spaying 1) Altering 2) Fixing 3) Sterilisation 4) Sterilization 
Neutering, from the Latin neuter (of neither sex), is the removal of an animal`s reproductive organ, either all of it or a considerably large part. The term is often used in reference to males whereas spaying is often reserved for females. Colloquially, both terms are often referred to as fixing. While technically called castration for males, in ....
The operation in a male or female cat where the reproductive organs are removed. This is often carried out between five and six months of age but can be done when the kitten is even younger (cats can reach sexually maturity at four months).
[n] - the sterilization of an animal
fixing 1 altering noun the sterilization of an animal; `they took him to the vet for neutering`