This is an irregular feature - both in frequency and oddness - dedicated to a word I came across that I have never previously used.
tentamen (TENT-ah-mehn) n. an attempt, experiment, or test to determine results through trial and error.
The plural form of this word is tentamina, and the word is of Greek origin, which has similar connotations. Most often this term is used in mathematics and philosophy to describe attempts to prove a supposition.
I came across tentamen in a Wikipedia article on Farkas Bolyai, a Hungarian mathematician who completed groundbreaking work on Euclid's parallel axiom.