The Collaborative International Dictionary of English v.0.48:

Tebeth \Te"beth\, n. [Heb.]
   The tenth month of the Jewish ecclesiastical year, answering
   to a part of December with a part of January. --Esther ii.
   16.
   [1913 Webster]

Easton's 1897 Bible Dictionary:

Tebeth
   (Esther 2:16), a word probably of Persian origin, denoting the
   cold time of the year; used by the later Jews as denoting the
   tenth month of the year. Assyrian tebituv, "rain."


Hitchcock's Bible Names Dictionary (late 1800's):

Tebeth, good, goodness (the tenth month of the Hebrews)