The Collaborative International Dictionary of English v.0.48:

Essene \Es*sene"\, n.; pl. Essenes. [Gr. ?, lit., physicians,
   because they practiced medicine, fr. Chald [=a]say[=a] to
   heal, cf. Heb. as[=a].]
   One of a sect among the Jews in the time of our Savior,
   remarkable for their strictness and abstinence.
   [1913 Webster]

Easton's 1897 Bible Dictionary:

Essenes
   a Jewish mystical sect somewhat resembling the Pharisees. They
   affected great purity. They originated about B.C. 100, and
   disappeared from history after the destruction of Jerusalem.
   They are not directly mentioned in Scripture, although they may
   be referred to in Matt. 19:11, 12, Col. 2:8, 18, 23.