atoll

English borrowed "atoll" from Portuguese atol, which came from Dhivehi atoḷu, the word used in the Maldives for these ring-shaped reefs. That Dhivehi word may trace back through Prakrit *saṃtīṭha to Sanskrit sam- plus tīrtha, meaning "level ford." An old theory linking it to Persian âb-tal ("water-hillock") is now considered unlikely.

The word traveled from the Maldivian islands themselves into Portuguese sailors' vocabulary, then into English, keeping its meaning as a ring-shaped coral reef throughout.

If the Sanskrit root holds, "atoll" is distantly tied to tīrtha, "ford" — a word about crossing calm, level water, fittingly echoed in the lagoon an atoll encircles.