I once listened to someone speak and at a particular point in their sentence, I thought they were going to say something very inappropriate for the context we were in. I felt that cringy feeling of embarrassment on behalf of another person. The speaker continued, finished her sentence well and communicated her message. No gaffe, no drama, no reason for my premature embarrassment. How so? I thought she was going to say a specific word. In fact, the word I thought she was going to use was the only one that made sense, to me at least, given the context of the words that came before it. However, she said something just like that word with the same first syllable and the exact same meaning but was totally appropriate.

This incident got me thinking about subclasses of synonyms like this and what to call them.  These words and phrases can all be grouped under the general genus of synonyms but they have some specific features and relationships that make them more special than other synonyms. These specific features warrant, in my opinion, specific taxonomy. I term these sets of word/phrase/expression pairs, Synonym Species. Below I offer pseudo formal definitions for three synonym species and provide accompanying examples.

Clumsy Synonyms
Definition: The set of word pairs, phrase pairs, or expression pairs that map to approximately the same meaning space but evoke different reactions when one is substituted for the other in a given context. 
One pair of phrases in this set is (“sheer amount”, “shit load”). These phrases are roughly synonymous and can be used interchangeably in a variety of contexts. However, in most religious contexts, substituting one for the other will evoke different reactions albeit they map to the same meaning space. 

Conditional Synonyms
Definition: The set of word pairs, phrase pairs, or expression pairs that are not inherently synonymous but become synonyms in a very specific context.
One example in this set is the pair, (“assault”, “battery”). The words are usually not synonymous in ordinary people speak but they map to roughly the same thing in a legal context.  

Temporally Transposed Synonyms
Definition: The set of word pairs, phrase pairs, or expression pairs that used to be synonymous at some point in the past but have now become antonymous over time.
I use “temporal” for this set to indicate the passage of time and “transposed” to indicate the reversal of meaning. These pairs used to mean the same thing but now mean the opposite. For example the pair, (“awful”, “awe inspiring”) used to mean the same thing. Many centuries ago “awful” literally translated to “filled with awe”. Now we use “awful” to refer to nouns that are a long distance away from being “awe inspiring”. 

There are probably a lot more of these synonym species to be explored but diving too deep will probably prove more costly than they’re worth although it would be very interesting to perform a linguistic analysis on synonym species collected from various languages.