neuropil

noun

neu·​ro·​pil ˈn(y)u̇r-ə-ˌpil 

variants also neuropile

-ˌpīl 

: a fibrous network of delicate unmyelinated nerve fibers interrupted by numerous synapses and found in concentrations of nervous tissue especially in parts of the brain where it is highly developed

neuropilar

-ˌpī-lər 

adjective