There are certain words that I normally cannot think of when I need to say them. I'll know what I mean to say, conceptually, but it is just remembering the word that gets me. List the ones that bedevil you, or should I say... which do not bedevil you.
Improvise - ironically, when I go blank on "improvise" I must improvise to find a substitute phrase.
There are some words that don't have any/many synonyms. If your word is one of these, you will have a harder time of it in these instances.
I had some others, but I cannot think of them at the moment now... What is the one that refers to someone being given a partial refund, and this word describes the process of the calculation required to do so ?