ser·ine (s?r??n?)n. An amino acid, C3H7NO3, that is a common constituent of many proteins.[ser(icin) + -ine.]American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.serine (?s?ri?n; ?s??ri?n; -r?n) n (Biochemistry) a sweet-tasting amino acid that is synthesized in the body and is involved in the synthesis of cysteine; 2-amino-3-hydroxypropanoic acid. Formula: CH2(OH)CH(NH2)COOH[C19: from sericin + -ine2]Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014ser?ine (?s?r in, -?n, ?s??r-) n. a crystalline amino acid, HOCH2CH(NH2)COOH, found in many proteins and obtained by the hydrolysis of sericin. Abbr.: Ser; Symbol: S [1875?80;