thre·o·nine 
(thrēə-nēn′, -nĭn)
(thrēə-nēn′, -nĭn)n.
A colorless crystalline amino acid, C4H9NO3, that is obtained from the hydrolysis of protein and is an essential component of human nutrition.
[Probably from threose, a kind of sugar (alteration of erythrose : ERYTHRO- + -OSE2) + -INE2.]