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.