The Collaborative International Dictionary of English v.0.48:

Tisri \Tis"ri\, n. [Heb. tishr[imac], fr. Chald. sher[=a]' to
   open, to begin.]
   The seventh month of the Jewish ecclesiastical year,
   answering to a part of September with a part of October.
   [1913 Webster]

Easton's 1897 Bible Dictionary:

Tisri
   the first month of the civil year, and the seventh of the
   ecclesiastical year. See ETHANIM (1 Kings 8:2). Called
   in the Assyrian inscriptions Tasaritu, i.e. "beginning."