Why is this so hard: premier/premiere?
The Young Victorian Theatre Company describes itself as “Baltimore's premiere professional summer theater company, specializing in Gilbert & Sullivan operettas.”
One might expect people involved in the theater to know that it’s premier (adj.) that means “first” or “foremost.” That’s why as a noun it is synonymous with prime [first, foremost] minister.
Premiere (n.) is a first performance of a work.
W.S. Gilbert would likely not be pleased.