menoversary 

The monthly recurring date of a past event, especially one of historical, national, or personal importance. Often referred to as a "month anniversary." This is wrong, because "anniversary" comes from the root "ano" meaning year, while "menoversary" comes from "meno" meaning month.

I asked my girlfriend out on October 24th, 2005. Our 1st menoversary is on Thanksgiving, and our 2nd menoversary will be on Christmas Eve.

menoversary by The One True Kaiser November 24, 2005

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

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

manaversary

When a husband chooses to spend his wedding anniversary with his friend instead of his wife.

A husband who forgets about a wedding anniversary, and spends the day with his friend instead if his wife. His Manaversary hopefully was worth it.

manaversary by Hater Wife February 24, 2014

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

mensiversary 

The monthly recurring date of a past event, especially one of historical, national, or personal importance

Me and my girlfriend are celebrating our first mensiversary next Friday.

mensiversary by TheNad September 4, 2009

moniversary 

When couples celebrate each month they have been together because they have not been together long enough to celebrate a real anniversary. A ritual annoying to some.

"Happy 3 month moniversary, Joe! Only nine more months until our one year anniversary."

"Uh, gee, thanks. Was I supposed to get you a card or something?"

moniversary by FGCUmomz July 28, 2009