An island in the river Anduin (LotR/812), translated “Ship of Long Foam” (PM/371), sometimes appearing as just Andros “Long Foam (LotR/1115). This name is a combination of cair “ship”, and “long” and ross “foam, spray” (SA/an(d), ros).
Conceptual Development: In Lord of the Rings drafts from the 1940s, this island was first named N. Tol Varad “Defended Isle”, soon revised to Men Falros “✱Place of Splashing Foam” (WR/326). Later in the drafts it was changed to N. Cairros “✱Ship Foam” then Andros before Tolkien settled on its full form N. Cair Andros (WR/340 note #15).
cair (“ship”), and (“long”) + ros (“foam, rain”) Nd doesn’t become nn before r; the original form of ros would probably be ross, with the final s dropped at the end of a polysyllable [HKF].