Is there any thing that is called synaptic neurotransmitter?

Yes, there are seven major neurotransmitters that each have a name: acetylcholine, dopamine, gamma-aminobutyric acid (GABA), glutamate, histamine, norepinephrine, and serotonin. https://www.mvorganizing.org/what-are-the-7-major-neurotransmitters/

That's what synapses are for: the release of neurotransmitters from the presynaptic cell into the synaptic cleft, where it interacts with a specific receptor on the cell at the other side of the synaptic cleft. As answered by another Doctor, there are several chemical structures that function as synaptic neurotransmitters. Dopamine, GABA, Serotonin & Epinephrine are some of the most well known.