Boyd’s Bible Dictionary:
Ninth month of the Jewish sacred, and third of the civil year, corresponding to parts of November and December (Neh. 1:1).
Strong’s Dictionary of Hebrew Words:
Meaning:
probably of foreign origin; Kisleu, the 9th Heb. month
Potts’ Bible Proper Names:
Rashness; confidence:―the ninth month of the Jewish sacred year, Zech. 7:1. {Temeritas}
From Manners and Customs of the Bible:
Nehemiah 1:1. It came to pass in the month Chisleu.
This corresponded very nearly to our month of December.