Ataptatanū (Sanskrit:अतप्ततनू) – tapa (तप) means – 'to burn', 'heat up'; atapta (अतप्त) – means - 'not heated', 'cool', and tanū (तनू) – means - 'body', 'the physical self'; ataptatanū means – 'he whose body or mass is not prepared in fire', 'raw' 
The compound word, ataptatanū, appears in the below cited mantra of the IX Mandala of the Rig Veda. In a sukta addressed to Pavmāna Somo Devatā, Rishi Pavitra prays:-
- पवित्रं ते विततं ब्रह्मणस्पते प्रभुर्गात्राणि पर्येषि विश्वतः |
- अतप्ततनूर्न तदामो अश्नुते श्रृतास इद्वहन्तस्तत्समाशत || (Rig Veda IX.83.1)
In this mantra, ataptatanūh, refers to the one who has not subjected himself to the heat of tapas, tadāmah refers to one who is raw and who therefore, aśunate - cannot experience the highest bliss because his body is not yet properly prepared to receive the knowledge he seeks.
In his Satyarth Prakash (Light of Truth), Swami Dayananda Saraswati explains that ataptatanū does not refer to branding with fire of one’s body which fact is clarified by Rishi Pavitra in the subsequent mantra which reads:-
- तपोष्पवित्रं विततं दिवस्पदे शोचन्तो अस्य तन्तवो वयस्थिरन् |
- अवन्त्यस्य पवीतारमाशवो दिवस्पृष्ठमधि तिष्ठन्ति चेतसा ||
and which means –
- " O Lord Thou Who art the Protector of the universe and the Veda, and art Omnipotent, Omnipresent, and Holy in nature canst not be approached by a human soul that has not been purified by tapa (or tapasya by means of thorough control of the senses, truthful speech, subjugation of the animal in man (instinct), conquest of the lower self, the practice of yoga, association with good men – all these constitute tapasya), and is therefore, not spiritually regenerate; it is only those, whose souls have been cleansed through righteous conduct and devotion to virtue, that can see Thee Who art All Holy. " (Rig Veda IX.83.2) 
Tapa or tapasya, is practical discipline; according to the Bhagavada Gita (XVII.14), revering the gods, the twice-born, elders, teachers and wise men, purity, celibacy, and non-violence these are the tapasya of the body, of speech and of mind. The finishing phase of a scholar’s higher education was called tapasya in the time of Krishna. Gandhi considered tapasya to be the test of love, ahimsa, self-suffering and self-sacrifice, essentials in the quest for truth.
- "Monier-Williams Sabskrit-English Dictionary".,
- Rig Veda with commentary in Hindi of Swami Dayananda Saraswati. Arya Samaj, Jamnagar. p. 272.
- Dayananda Saeaswati. Light of Truth-Satyarth Prakash. Sarvadeshik Arya Pratinidhi Sabha. p. 369.
- Bhagavad Gita. Islamkotob. p. 240.
- Alo Shome. Krishna Charitra. V&S publishers. p. 55.
- Raghavan Iyer. wisdom in Action. Theosophy Trust. p. 254.