Proper noun
Marcheshvan
(Judaism) Cheshvan
In a malei ("filled") year, the month of Marcheshvan is increased to 30 days. 13-month years follow the same pattern, with the addition of the 30-day Adar Alef, giving them between 383 and 385 days. Source: Internet
The month you ask about is consistently referred to in halachic discussions as Marcheshvan, not Cheshvan. Source: Internet