Month

A month was a unit of time measurement. According to the Fourth Doctor — who was almost certainly speaking of its duration on Earth — a month lasted 2,678,400 seconds. (TV: The Brain of Morbius)

Months had individual names. Known months — not all of which were Earth months, and so not all of which could possibly equal 2,678,400 seconds — included: allowcachedresults=true category=DWU months columns=6

Behind the scenes
Though he doesn't specify in the script of Morbius, the Doctor's sums reflect a 31-day month.