'tad' originates from the early 20th century American English, possibly derived from 'tadpole,' where 'tad' was a colloquial term for a small child or a small amount.

'tad' was used in American English to refer to a small child, and eventually became a term for a small amount or degree.

Initially, it meant 'a small child,' but over time it evolved into its current meaning of 'a small amount or degree.'