Synonyms - how does it work?

If I see some competitor which has on page seo for a synonym for a keyword I'm targeting it means that google will treat it equally (put aside the other parameters I mean ofc)?
I'm asking because I don't think software like market samurai put it into consideration.

Any takes on the matter would be appreciated

EDIT: just to sharpen my question, what I mean is if I see another site did seo for a synonym of a keyword should I treat it as "oh nice I can optimize for my keyword" or "damn he optimized for a synonym it's basically the same" - thanks!

Yes, but that ability of Google is getting stronger by the way. You can't say that Google applies this to all the synonyms as we find in thebestspinner or other spinning programs.

Google only does this for absolute synonyms (The most relevant ones) This is only to make it easier for searchers, but Google is being very careful about this.

I just answered another similar question by you.

Use of keyword depends on user completely... If your user is using 'nation' as his keyword instead of 'country', Google will display only sites which are optimized for keyword 'nation'.

This is why including synonym keywords is always appreciated.