N5 — outside your level filter
数＋月
Needs a numeral in front of it and takes no copula, so there is no paradigm to conjugate.
月
gatsumonth (counter)N5counter
Readings and definitions from JMdict, © the Electronic Dictionary Research and Development Group (EDRDG), used under CC BY-SA 4.0; the words themselves come from the Tanos JLPT lists.