tryp·to·phan (tr?p?t?-f?n?) also tryp·to·phane (-f?n?)n. An essential amino acid, C11H12N2O2, formed from proteins during digestion by the action of proteolytic enzymes. It is necessary for normal growth and development and is the precursor of several substances, including serotonin and niacin.[trypt(ic), of trypsin (formed on the model of pepsin, peptic); see trypsin + -phan(e).]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.tryptophan (?tr?pt??fæn) or tryptophanen (Biochemistry) an essential amino acid; a component of proteins necessary for growth[C20: from trypsin + -phan from Greek phain? appear]Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014tryp?to?phan (?tr?p t??fæn) also tryp?to?phane (-?fe?n) n. an essential amino acid, (C8H6N)CH2CH(NH2)COOH, released from proteins by the enzyme trypsin during digestion. Abbr: Trp;Symbol: W [