IPA: //ˌʌn.ɪkˈsaɪ.tə.bəl//
KK: /ʌnɪkˈsaɪtəbl/
Someone who does not get excited easily or remains calm in situations that might cause others to become excited.
Despite the chaos around him, he remained unexcitable and focused on his work.
Unexcitable → It is formed from "un-" (meaning not) and "excitable" (from Latin "excitare", meaning to rouse or stir up). The word "unexcitable" means not able to be roused or stirred up emotionally.
Think of 'not' ('un-') being able to 'stir up' ('excitable') emotions — that's why unexcitable means someone who remains calm.