From Tolkien Gateway
-ndil, -nil, -dil is a Quenya suffix added to names to indicate friendship, love, or devotion to an object, idea, grouping, course, occupation or spirit (Ainur) to which one is devoted for its own sake
nildo means "friend".
- Eärendil/Eärnil = "Devoted to the Sea"
- Amandil = "Friend of Aman"
- Ornendil = "Friend of the Trees"
- Valandil = "Devoted to the Valar"
- Elendil = "Friend of the stars", also understood as "Elf-friend"
- *Vardilmë = Possibly female form meaning "Friend of Varda"
- It also appears in Sindarin Edennil (adan) and Enerdhil (anar)