The Oxford Dictionary describes a 'symbol' as a: '1. thing regarded as typifying or representing something . 2. mark, sign, etc. representing an object, idea, function or process; logo.' And I guess that's a start... I'd say that the notions of 'carrier of meaning' and 'referring,' or 'representing' are crucial elements in the definition. So a symbol could be described as a thing that carries a meaning that refers to, or represents, the meaning of another thing.
David Fontana uses 5 categories of symbols, which is quite useful. He distinguishes:
- Shapes and Colours,
- Nature and the elements,
- Human & spiritual symbols.
Lots of symbols have been added to the database; currently there are over 300 definitions. Use the search facility to find them.