How do people feel about words such as "Subway", "Underground", "Luas", "Tube" etc. being accepted for "meitreo" ? I haven't reported any yet, but (save for Luas) the words are quite synonymous. The Metro lives in Paris, and nobody says "metro" in London or NYC.
The several synonyms seem reasonable to me. (Washington and Moscow also have Metro systems.) I suppose that “rapid transit” would be the generic term.
Unless one listens closely, it's difficult to tell this apart from "Cailleann sé an ticéad ar an meitreo"