Easton's 1897 Bible Dictionary:

Nicolaitanes
   The church at Ephesus (Rev. 2:6) is commended for hating the
   "deeds" of the Nicolaitanes, and the church of Pergamos is
   blamed for having them who hold their "doctrines" (15). They
   were seemingly a class of professing Christians, who sought to
   introduce into the church a false freedom or licentiousness,
   thus abusing Paul's doctrine of grace (comp. 2 Pet. 2:15, 16,
   19), and were probably identical with those who held the
   doctrine of Baalam (q.v.), Rev. 2:14.


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

Nicolaitanes, followers of Nicolas