There is actually no word in the English language spelled "trinest." Perhaps you meant "trimester"? This word is spelled T-R-I-M-E-S-T-E-R, and it is pronounced /traɪˈmɛstər/. The word refers to a period of three months, typically used to divide a school year or a pregnancy. Make sure to double-check your spelling when using words that are unfamiliar or uncommon to avoid confusion and miscommunication.