For a definition of the term dṛṣṭānta see, for example, Carakasamhita Vimanasthana 8.34 (in the ed. of Trikamji):
atha dṛṣṭāntaḥ — dṛṣṭānto nāma yatra mūrkhaviduṣāṃ buddhisāmyaṃ, yo varṇyaṃ varṇayati. yathā — agnir uṣṇaḥ, dravam udakaṃ, sthirā pṛthivī, ādityaḥ prakāśaka iti; yathādityaḥ prakāśakas tathā sāṅkhyajñānaṃ prakāśakam iti.
Oberhammer's (Unter Mitarb. von Ernst Prets und Joachim Prandstetter) Begriffswörterbuch, vol. 2, which I do not have at my desk, should provide additional references s.v. dṛṣṭānta.
With kind regards,
Philipp