I’m taking my first math-intensive class in two and a half years, and it’s lit a fire under some words and concepts that had lain dormant for a while. I once again have reason to say things like “big-O notation” or “norm”, I assure you I am doing so to my heart’s content. But at the same time, it’s opening up scabbed-over questions of usage. The one that was gnawing on my mind during class today was: is an easy math problem soluble or solvable? Thankfully for the thesaurer in me, it’s both (or at least that’s what the OED says). In fact, soluble can also refer to something that can be loosened or untied, such as a soluble knot, in addition to something that can be solved (a soluble problem) or dissolved (a soluble powder).
And, in case you were wondering, thesaurer (meaning “one who makes thesauruses”) is of questionable derivation; it is actually an archaic form of treasurer. However, thesaurus means both “book containing a lot of synonyms” and “room containing a treasure”. A thesaurer is clearly defined as someone who lords over a thesaurus (the second definition), so it’s not great leap to extend its definition to include one who lords over a thesaurus (the first definition). You might object that there is no need for a new word here, as one who composes a thesaurus is a lexicographer. Wikipedia, for instance, considers Peter Mark Roget (of thesaurus fame) a lexicographer.
Of course, your objection would be ill-founded, because the lexicographer in me would balk at the thought of putting two identical words in his dictionary, whereas the thesaurer in me would revel in the opportunity to add more words to his thesauri (and that is the proper plural form, according to the OED). So clearly a thesaurer is not merely a lexicographer.