Well, the 'synonym back story' can be quite interesting. Take the words 'happy' and 'glad'. Their back stories may be related to cultural and historical usage. In different regions or time periods, one might have been more popular than the other. It could also be related to how the human perception of positive emotions has been expressed through language, which led to these two words having very similar meanings.
Sure. Consider 'wise' and 'clever'. The back story might be that 'wise' has an older origin and often implies a deeper, more profound knowledge and good judgment, perhaps with roots in Old English. 'Clever', on the other hand, might have developed later and often emphasizes quick - wittedness or ingenuity in a more practical or immediate sense.
The words 'don't mention it' were 'don't talk about it, don't mention it, don't mention it, keep your mouth shut, hide it in the bottom of your heart, remain calm, and keep your mouth shut.
Synonym fiction refers to fictional works that play with synonyms. It might involve using many different words with similar meanings to create a rich and nuanced language in the story. For example, instead of just using the word 'happy', the author could use 'joyful', 'elated', 'gleeful' etc. throughout the text to add variety and depth to the description of a character's mood.