IPA: /ɪmˈprɒp.ər.aɪ.ti/
KK: /ɪmˈprɑːpəˌrɪti/
A behavior or action that is not proper or acceptable in a social or moral context.
The committee discussed the impropriety of his comments during the meeting.
Impropriety is formed from "im-" (meaning not) and "proprius" (from Latin, meaning one's own or proper) and the suffix "-ety" (indicating a state or condition). The word refers to a state of being not proper or inappropriate.
Think of 'not proper' ('im-' means not and 'proprius' means proper) to remember that impropriety refers to something inappropriate.