Front of card:
死の間際＝死の寸前＝死の直前
Back of card: Everything in just hiragana, and Japanese definitions if needed.

This "format" came forth when I ran across the phrase 「死の間際」. When I looked up 「間際」, the two synonyms listed in the definition were 「寸前」と「直前」。Since I suspected 「間際」was not as common (at least concerning the target phrase) as the other two, I did a google search for 「死の直前」(most popular)と「死の寸前」と「死の間際」(least popular).

The reason why I included all three in my sentence/phrase in my SRS is that I wanted to add the original 間際 phrase、but I also wanted to include the more common ones, AND in the same context and same SRS item because I like to see the connection between them together and not separated throughout the deck. Also, I'm aware that the three synonyms are not exactly synonyms. 直前 has a more basic meaning of "just before" and 寸前　has a more elaborate meaning of "on the brink of/verge of," so I'm assuming in more cases than 直前、it would have a more negative feeling. (an exception would be 出発の寸前）

Of course, a format like this is probably not something to be forcefully produced (suddenly we're talking about constipation?). It should probably come out naturally as you see synonyms that interest you.

Any cons? I can see too many kanji in one SRS item as a slight con. Another con is that recognizing the subtle differences between each synonym may become an overload. It would also be good to use each synonym in different sentences to better establish how their differ from each other.

Anyway it's not a breakthrough or anything XD I'm sure someone's done it before anyway~

Sounds a bit dangerous if you don't have a real context for the synonyms. For example according to wwwjdic 間際 can be an adverbial noun but 寸前 is not. If you don't know how each word is used you may be making up ungrammatical sentences. Which is why I think getting all your sentences from native sources is a good idea.

Thanks for the input! Maybe the "=" thing is not a good idea then. I did add separate sentences for each "synonym" though so hopefully it won't be so risky~

Hi, your format is not really new. Basicaly all my sentences are like this:

front: All kanji sentence.

back: hiragana sentence + definitions in Japanese, listing the synonyms and antonyms.

The reason I do that is that synonyms and antonyms generally already come in the definitions of words in sainseido.net's dictionary. I just don't bother to remove them.