A notional unit of time (typically reckoned as 1/7 of a year) based on the supposed ratio between the average lifespan of a dog and that of a human; (hence, in plural) a (seemingly) long time.
Origin
1930s.
Definition of dog year in US English:
dog year
noun
North American
A notional unit of time (typically reckoned as 1/7 of a year) based on the supposed ratio between the average lifespan of a dog and that of a human; (hence, in plural) a (seemingly) long time.