'tax-deductible' originates from the combination of 'tax' and 'deductible', where 'tax' refers to a compulsory financial charge and 'deductible' means capable of being deducted.

'tax-deductible' evolved from the concept of 'deductible' expenses in tax law, becoming a common term in modern financial language.

Initially, it referred to any expense that could be subtracted from income, and this meaning has remained consistent in modern usage.