From taking the synset of the word 'fantastic', I got a list of senses below:
[Synset('antic.s.01'), Synset('fantastic.s.02'), Synset('fantastic.s.03'), Synset('fantastic.s.04'), Synset('fantastic.s.05')]
What does 's' stand for?
Another example, taking a synset of the word 'fast':
[Synset('fast.n.01'), Synset('fast.v.01'), Synset('fast.v.02'), Synset('fast.a.01'), Synset('fast.a.02'), Synset('fast.a.03'), Synset('fast.s.04'), Synset('fast.s.05'), Synset('debauched.s.01'), Synset('flying.s.02'), Synset('fast.s.08'), Synset('firm.s.10'), Synset('fast.s.10'), Synset('fast.r.01'), Synset('fast.r.02')]
Again what does 's' stand for? And also what does 'r' stand for?