halfaversary 

The celebration of a half-year since something important occured.

Katherine: Oh my gosh, Doug, it's August 15th! We started dating on February 15th... do you know what that means?! Today is our halfaversary!
Doug: Oh, that's right. You're dumb, but happy halfaversary.

halfaversary by Eillek Nagrom January 16, 2008

halfiversary

A couple's 6 month anniversary (similar to a half birthday).

Prem and Becky got married on July 11th, so they celebrated their halfiversary on January 11th.

halfiversary by Premdawg January 12, 2011

Halfiversary

Like an Anniversary, but a celebration for six months in a relationship, friendship, etc..

Hey babe, its been six months! Happy Halfiversary!!

Halfiversary by Anonymously Jay October 13, 2016