inexcitable

adjective

in·​ex·​cit·​able ˌin-ik-ˈsīt-ə-bəl 

1

: not readily excited or aroused

2

of a nerve : not subject to excitation : not responsive to stimulation

inexcitability

-ˌsīt-ə-ˈbil-ət-ē 

noun

plural inexcitabilities