This type of synapse is constricting, inhibitory, it is "inhibitory", they say. "Slowing" means, in this context, that synaptic activity reduces the likelihood of a nerve impulse/action potential being triggered in the initial (axon) segment (IS) of the affected postsynaptic neuron.
Axon ends/boutons that give rise to inhibitory synapses, so-called." Synapse type II", contains flattened synapse vesicles. The postsynaptic membrane is not thickened.
Inhibitory synapses rarely engage dendritic tags, and are common at the dendrite bases, on the cell body and on the initial axon segment (IS) itself where they have a particularly strong impact.
The most common inhibitory transmitter substance is GABA.