1. Excellent
   "he did a slap-up job";
   - bang-up [N. Amer, informal], bully [informal], corking [Brit, informal], cracking [Brit, informal], dandy [informal], great, groovy [informal], keen, neat, nifty [informal], not bad [informal], peachy, swell [informal], smashing [Brit, informal], old, not half bad [informal], grouse [Austral, NZ, informal], ripper [Austral, informal], lovely
    
2. [Brit, informal] (of a meal) excellent and lavish
   "We had a slap-up dinner to celebrate"

See also: good, lavish, lucullan, plush, plushy