trialist

Short definition from Wiktionary

Noun

1. 1
   An advocate of trialism, especially with reference to the proposed creation of a state comprising Austria, Hungary, and a Slavic region.
2. 2
   A person who takes part in a clinical trial, especially as a researcher.
3. 3
   A person who tries a product for the first time (as opposed to a regular purchaser); a person who participates in the trial of a new product.
4. 4
   An athlete who participates in a trial (competition to select players for a team); a person who enters a dog (especially a sheepdog) in a competition.
5. 5
   A person standing trial in a court of law, especially one of a group of defendants in a high-profile case.

Adjective

1. 1
   Involving three elements; especially, pertaining to a potential state comprising Austria, Hungary, and a Slavic region.