"A library book."

Translation: Leabhar leabharlainne.

[IsMiseArron]

Why not leabhar na leabharlainne?

[Baloug]

Because it would mean "the library's book", i.e. a book from a specific library, whereas leabhar leabharlainne just means the book is from an undefined library.

[AnneNoone1]

I just wrote "leabhar labharlainne" looked up library. So corrected library to (leabharlann) who is right foclóir Gaeilge or Duolingo. Just trying to get spelling right. Pls help. Go raibh maith agat

[SatharnPHL]

You are using "library" as an attribute of "book", as though it was an adjective. To use a noun as an attribute of another noun in Irish, you use the genitive of the attributive noun.

Your foclóir Gaeilge will tell you that leabharlainne is the genitive of leabharlann, so that the Irish for "a library book" is leabhar leabharlainne.