An Cat Dubh is Gaelic and means "black cat".
Jonas Steverud (Maintainer of U2MoL) (contributed before the 20:th of February 1998)
I heard a live bootleg on which Bono introduces this song by talking about how everyone has some darkness inside of them. For me, the song certainly evokes that sense of duality.
Richard Lim rlimis.dal.ca (contributed before the 20:th of February 1998)
I heard Bono say in a recording of a concert that this song refers to how some things can be beautiful but dangerous. In "Into the Heart: The Songs of U2", Niall Stokes quotes both Bono and Gavin Friday talking about how the song is about a fling that Bono had with a Gaelic girl in high school during a brief break-up with Ali (who he is now married to). Bono also talks about the image of a cat who kills a bird and plays with it and them lies down to sleep beside it. He says that he was actually the black cat.
Melanie Colenutt melaniecolenutthotmail.com ( 2:nd of April 2001)