Foinaven SLUR is used here as a musical term. Think of a three letter word for a gun, usually associated with America, and a four letter word for decoy.
MAYBE TELL tell is the definition, but not in relation to speaking. Second definition in Chambers.
I feel very foolish. I have completed everything bar the first letter of the down clue CHARACTERS. Please can someone put me out of my misery?
A very clever grid fill. Thank you, Shark.