From WordNet (r) 3.0 (2006) [wn]:
instructor
n 1: a person whose occupation is teaching [syn: teacher,
instructor]
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]