Almost all of the words you mentioned match the concept, but I feel none is the one escaping me.
I have put this forward on Ask.com and have received answers, some in common with yours, but none fit the bill; like, sangfroid.
I don't know. Maybe one of those was just what I'm after and I don't get it.
Tromboniator said: Gosh, I often find a thesaurus to be very useful to find what I need
Yeah, me too. And also rhyming dictionaries. Why, just yesterday I was composing a birthday limerick for my mom. Needed a word that rhymed with "osh" for the last line and it helped me find panache (which was in my vocab but rarely used).
And when writing on MS Word, I often find myself using TOOLS / LANGUAGE / THESAURUS to find a synonym that just works better or allows me to avoid repeating myself.
I suspect Robert's comment about "thesaurus smells" relates to poorly chosen synonyms in translations, but anyone who translates should be fairly proficient in both languages or they wouldn't be in that business.
Then again, I'm reminded of the often poor (and sometimes unintentionally amusing) translations I see in instructions for products manufactured in Japan or China. Makes one wonder if those are written by real translators, or just engineers that understand the product more than they do the English language.