Meaning of second messenger

sec'ond mes'senger

Pronunciation: [key]
— Biochem. Biochem.
  1. any of various intracellular chemical substances, as cyclic AMP, that transmit and amplify the messages delivered by a first messenger to specific receptors on the cell surface. Cf.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.