eka-deśaṁ tu vedasya vedāṅgāny api vā punaḥ yo 'dhyāpayati vṛtty-artham upādhyāyaḥ sa ucyate

"One who teaches others a part of the Vedas or literatures supplementary to the Vedas may be called upadhyaya." Upadhyaya also refers to one who teaches art.