What is the past tense of cost?

The past tense of cost is cost.

Cost is unchanged in the past tense.

All forms of cost

as a noun

base: cost
plural: costs

as a verb

base: cost
past tense: cost
past participle: cost
present participle: costing
third-person singular: costs

Cost in a sentence

Therefore, it is necessary to reduce the cost.CM
This dictionary, of which the third volume is missing, cost me a hundred dollars.Zifre
Because of inflation, salaries can't keep up with the high cost of living.CM