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).
He who, being (duly) chosen (for the purpose), performs the Agnyadheya, the Pakayagnas, (and) the (Srauta) sacrifices, such as the Agnishtoma (for another man), is called (his) officiating priest.
उपाध्यायान् दशाचार्य आचार्याणां शतं पिता । सहस्रं तु पितॄन् माता गौरवेणातिरिच्यते ॥ १४५ ॥
The teacher (akarya) is ten times more venerable than a sub-teacher (upadhyaya), the father a hundred times more than the teacher, but the mother a thousand times more than the father.