Annuity derives from Latin annus, meaning year. The Medieval Latin form annuitas meant a yearly payment or annual income, and English borrowed it in the 15th century for a financial arrangement that provides a fixed sum at regular intervals, typically annually. The word shares its root with annual, anniversary, perennial, and biennial — all words built around the Latin year.
The concept is much older than the English word. Roman law recognized annuities as financial instruments, and the jurist Ulpian compiled one of the earliest actuarial life tables around 220 AD to help calculate their value. His table estimated how many more years a person of a given age could expect to live, allowing courts to determine the present value of promised future payments in inheritance disputes.
Medieval European monasteries used annuities extensively. A donor would give a lump sum to a religious house in exchange for guaranteed annual payments for life — essentially a retirement income. After the donor's death, the monastery kept any remaining capital. This arrangement funded monastic operations while providing financial security to aging benefactors. It was, in effect, an early pension system operated by the church
Modern annuities are sold primarily by insurance companies and function as retirement income products. The purchaser pays a lump sum or series of payments, and the insurer guarantees regular income for a specified period or for life. The underlying mathematics — calculating present value based on interest rates and life expectancy — is essentially what Ulpian was doing in 220 AD, refined with eighteen centuries of additional actuarial science.
The Latin root annus may connect to a Proto-Indo-European root meaning to go or to go around, reflecting the ancient perception of the year as a cycle — a journey that returns to its starting point. This circular concept is preserved in anniversary, literally a turning of the year.