tryptophan

noun

1. (countable, uncountable)An essential amino acid with an indole side chain; present in many foods, especially chocolate, oats, banana and milk; it is essential for normal growth and development and is the precursor of serotonin and niacin; any specific form of this compound, or any derivative of it.

   “The quickest way to raise serotonin levels again is to send more tryptophan into the brain, because serotonin is made from tryptophan.”

   “Tryptophan is an amino acid found in many foods, including dairy and turkey, which is one of the reasons commonly given for why so many of us feel so sleepy after our Thanksgiving feasts.”