IPA: //ʌnˈsɛnsaɪtɪd//
KK: /ʌnˈsɛnsaɪtɪd/
Not made sensitive or responsive to stimuli or influences.
The unsensitized material did not react to the light exposure.
Unsensitized → It is formed from "un-" (meaning not) and "sensitize" (from Latin "sensibilis", meaning able to feel). The word means not made sensitive or not able to feel.
Think of 'not' ('un-') making something 'able to feel' ('sensitize') — that's why unsensitized means not able to feel.