MoniLac is a rare Runeword created by combining a Moni Rune of Ritual and a Lac Rune of Invocation.
How to Create MoniLac
You can create MoniLac by adding the magic Moni Rune of Ritual and the rare Lac Rune of Invocation to a two-socketed 
Helm, 
Chest Armor, 
Pants, or 
Two-Handed Weapon.
Challenging ShoutOverflow
MoniLac can not overflow because the amount of Offering you receive from the Moni Rune exactly fills the required Offering of the Lac Rune.
Overflow occurs when your Ritual generates more Offering than required for the Invocation. The overflow effect is proportional to the amount Offering overflows.
Legions
Helltide