noun
: a cellular substance (as cyclic AMP) that mediates cell activity by relaying a signal from an extracellular molecule (as of a hormone or neurotransmitter) bound to the cell's surface
noun
: a cellular substance (as cyclic AMP) that mediates cell activity by relaying a signal from an extracellular molecule (as of a hormone or neurotransmitter) bound to the cell's surface
Webster's New International English Dictionary. Новый международный словарь английского языка Webster. 2012