Never a cross word...

I've managed to practically finish the Sunday supplement crossword, but there is no clue for 23 down.

It's a 4-letter word. S-something-L-something. Hmm...

If I want to enter into the competition, should I leave it blank or make something up? Perhaps I'm in with a better chance of winning if I come up with a less obvious solution...

Self
Salt
Silt
Sole
Sale
Silk
Silo
Solo
Sold