# I am not able to be susceptible

My prefix is used half the time,
My infix is self-referencing;
My suffix is a group of adults,
My whole is an agreement.

What am I?

My prefix is used half the time,

am - ante meridiem or before midday

My infix is self-referencing;

me - refers to myself

My suffix is a group of adults,

• Brilliant. ${}$ – TheSimpliFire Mar 7 '20 at 18:47