Pet that won’t get pregnant until married (3)

I believe the answer is:
tom
'pet that won't get pregnant' is the definition.
The answer and definition can be both animals as well as being singular nouns.
Maybe there's a link between them I don't understand?
'until married' is the wordplay.
'until' becomes 'to' (I've seen this in other clues).
'married' becomes 'm' (abbreviation, e.g. in genealogy).
'to'+'m'='TOM'
Can you help me to learn more?
(Other definitions for tom that I've seen before include "Queen's mate" , "Bell" , "famous schoolboy" , "queen's consort?" , "Cruise" .)
