Spoil: 1. I've got some ham that'll spoil if we don't eat it tonight. 2. She was afraid of spoiling Christmas for the rest of the family. 3. I wouldn't want to spoil your fun Ruin: 4. It was a large white house falling into gentle ruin. 5. In Tolkien's world, evil is the antithesis of creativity, and is dependent on destruction and ruin for its basis. 6. One atom bomb had created as much ruin and misery as hundreds of airplanes had. In (1) and (3) we can only use 'spoil', but in (2) you could substitute 'ruining'. In (4) and (5) and (6) you can only use 'ruin'. Generally food 'spoils' while buildings 'fall into ruin'. But check out these links for more nuance: - https://en.oxforddictionaries.com/definition/spoil - https://en.oxforddictionaries.com/definition/ruin Hope that helps a little. :-)