From WordNet (r) 2.0 (August 2003) [wn]:
instructor
n : a person whose occupation is teaching [syn: teacher]
From The Collaborative International Dictionary of English v.0.48 [gcide]:
Instructor \In*struct"or\, n. [L., a preparer: cf. F.
instructeur.] [Written also instructer.]
One who instructs; one who imparts knowledge to another; a
teacher.
[1913 Webster]