3, as Malone says, it’s D(ail)Y + (i)S + ON (just after), which is in Chambers
4, definition is peremptory, as in final, SOL (solicitor) in A BUTE, short for phenylbutazone, an anti-inflammatory drug used on horses.
Actually I think Bute masks pain to make horses run faster, and nobblers would be attempting the opposite, but what do I know? The dictionary says phenylbutazone is used in horse-doping, so maybe that excuses it