### Clue: Product of Tesco, it's added to and enlarges one like itself (5)
### Answer: COSET 
 ### Explanation: Definition: it's added to and enlarges one like itself
TESCO* – a coset is a concept in the theory of mathematical Groups, but the definition here mirrors the one given in Chambers: "a set which when added to another set resuts in a larger set", which is not particularly meaningful.