Menniversary 

The day of celebration in monthly installments after a given event; an anniversary, but monthly instead of yearly

You mean your one-month menniversary, because 'anniversary' makes no sense when its less than a year.

Menniversary by twlhisdvkljh October 9, 2010

mensiversary 

MEN-SI-VER-SA-RY (mèn´se-vûr´se-rê) noun
1. The monthly recurring date of a past event, especially one of
historical, national, or personal importance: a first date
mensiversary; the mensiversary of the founding of Nerstone Pictures.
2. A celebration commemorating such a date.
from Latin: mensis, month + versus, past participle of vertere, to turn.

If the word for the commemoration of a yearly event is anniversary, by
analogy the logical word for the commemoration of a monthly event
should be "mensiversary." "Anniversary" comes from the Latin "annum,"
meaning year. (The "versary" part comes from a Latin word referring
to turning.) The Latin word for month is "mensis." Hence,
mensiversary. I've not found this word in any reputable dictionary,
but perhaps exposure in Google Answers can help to put it there.

Credit to pinkfreud-ga @ google answers

My girlfriend and I just celebrated our first mensiversary.

On November 2nd, the 8th mensiversary of our family reunion in Chicago, my family and I decided to take another trip back to visit the sites.

mensiversary by BeefnCheez November 11, 2007

manniversary 

The anniversary of a transgender man's transition beginning. Often marking his first testosterone shot, when he began binding/dressing in male clothes, or whatever he decides 'began' his transition.

Have you seen the FTM 1 year manniversary videos on youtube?

It's amazing how much muscle and hair growth he has-it's only his first manniversary!

manniversary by Ifreyja Vonneu February 1, 2017

manniversary 

Yearly celebration of wedding day of two gay males.

This year, Brad and Josef will be celebrating their third manniversary, though the memories of their Fire Island wedding are as vivid as if it had happened yesterday.

manniversary by OhPuhLeez February 23, 2005

miniversary

Like an anniversary, a date marking the successful passage of time in a relationship.

They've been going out one week and already have celebrated their first miniversary.

miniversary by P-fizzy December 14, 2005

mensiversary 

Of a significant event, a day that is an exact number of months (to the day, if possible since months have different numbers of days - this conflict obviously doesn't occur with an anniversary) since the event occurred; often preceded by an ordinal number indicating the number of months that have elapsed since the event.
(Keep in mind, this is not a real word, but it could be considered etymologically correct according to Latin and similar derivation to anniversary.)

Could be considered synonymous to lunaversary, a more common fake word for a reoccurring monthly event, but this is less etymologically correct by indirect induction of roots.

WRONG: Happy two-month anniversary!
RIGHT: Happy second mensiversary!

mensiversary by maelstr0m_X1 November 29, 2006

manniversary 

The day to be remembered when to guys became good friends. Often celebrated with heavy drinking,throwing up, and passing out. The day itself is usually forgotten due the drunken haze of the day so it is celebrated around the same general time each year.

Joe1: You know Joe it was around Labor Day last year we hung out out at your place and got shit faced, Good Times

Joe2: Your right and its about that time of the year now. Happy Manniversary bro.

Joe1: Happy Manniversary

manniversary by DrinkinBuds September 6, 2009