Boyd’s Bible Dictionary:
(goodness). Tenth month of Hebrew sacred, and fourth of civil, year; commencing with new moon in January (Esther 2:16).
Strong’s Dictionary of Hebrew Words:
Meaning:
probably of foreign derivation; Tebeth, the tenth Heb. month
Potts’ Bible Proper Names:
Good; goodness:―tenth month of the Hebrew sacred year; fourth of civil year, Esth. 2:16. {Bonus}
From Manners and Customs of the Bible:
Esther 2:16. The tenth month, which is the month Tebeth.
This corresponded very nearly to our month of January.