Difference in Acharya, Upadhyaya, Guru

Question

While explaining duties, Bhishma explains to Yudhistira that:

One Acharya is superior to ten Brahmanas learned in the Vedas. One Upadhyaya is again superior to ten Acharyas. The father, again, is superior to ten Upadhyayas. The mother again, is superior to ten fathers, or perhaps, the whole world, in importance. There is no one that deserves such reverence as the mother...In my opinion, however, the preceptor is worthy of greater reverence than the father or even the mother.

What is difference between Acharya, Upadhyaya, Guru... and may be similar words like adhyapaka. All roughly translate to teacher/tutor.

Karna had Drona as teacher but Parashurama is his Guru. Bhishma learnt from bhrihaspati but Parashurama was his guru. Guru is one who makes you complete as person... Of so, what about the others like acharyas, upadhyaya,...? We call Shankara, Madhwa, Ramanuja, etc. as acharyas but upadhyaya is superior to them? Any examples for upadhyayas?

Note: this is more of a language question than scriptures. Hence generic explanations will be accepted as answers.

Answer 1

One who initiates the pupil into Gayatri is called the Acharya.

Manu Smriti 2.140. They call that Brahmana who initiates a pupil and teaches him the Veda together with the Kalpa and the Rahasyas, the teacher (acharya, of the latter)

Upadhaya:

2.141. But he who for his livelihood teaches a portion only of the Veda, or also the Angas of the Veda, is called the sub-teacher (upadhyaya).

And finally Guru:

2.142. That Brahmana, who performs in accordance with the rules (of the Veda) the rites, the Garbhadhana (conception-rite), and so forth, and gives food (to the child), is called the Guru (the venerable one)

Answer 2

Gradation of teachers based on teaching levels :

1. The teacher who gives you information only is ....... Adhyapak

2. The one who imparts knowledge by combining information is....Upadhyaya

3. Skills are imparted by ....."Acharyas". Composers and teachers of bhashyas are also called Acharya

4. The teacher who is able to give an insight into the subject is ......"pundit"

5. The master who has a futuristic view on the subject and teaches you to think in that manner is ....."dhrishta"

6. The superior master who is able to impart wisdom of Atman in you is the ....."GURU'.

Answer 3

Skanda Purana has below definitions:

53. A Brāhmaṇa should perform the Upanayana rite of his disciple and teach him the Vedas along with all its esoteric secrets and the Kalpa. Scholars consider such a Brāhmaṇa an Ācārya.

54. A person who teaches a part of the Śruti or the Aṅgas (ancillary subjects) for the sake of maintenance of his livelihood is considered an Upādhyāya by scholars.

55. A Brāhmaṇa who duly performs the rites of Niṣeka etc. and maintains (disciples) with cooked food is glorified as a Guru.

56. On being invited (by a householder), if any learned Paṇḍita performs the rite of Agnyādheya (the rite of kindling holy fires), Pākayajñas (Aṣṭaka etc.) and the sacrifices of Agniṣṭoma etc., he is called his Ṛtivk.

57. From the point of venerability, an Ācārya is ten times greater than an Upādhyāya; father is a hundred times venerable than an Ācārya and mother a thousand times more venerable than father.