While this has been answered multiple times, submitted for your perusal, an earlier thread from2010 on the subject.
I’ve also in some occasions heard an (older) 1C1R referred to as an ‘aunt’ or uncle.’ In “The Beverly Hillbillies,” “Uncle Jed” was actually Jethro’s 1C1R. (That was just a TV program, but I have actually heard this IRL.)