Small working horse

Wikipedia Word definitions in Wikipedia
A pit pony was a type of pony commonly used underground in coal mines from the mid-18th until the mid-20th century. Ponies began to be used underground. The first known recorded use in Great Britain was in the Durham coalfield in 1750. The use of ponies ...

Longman Dictionary of Contemporary English Word definitions in Longman Dictionary of Contemporary English
noun EXAMPLES FROM CORPUS ▪ He had spent his working life down the local pit and drove a pit pony when he first went underground.