Vastu Purush Mandala having 45 Devtas and Asuras.
Aditi is a vedic goddess, found mentioned in the vedas many a time, and is also mentioned with respect to the Adityas. that are progeny of Aditi.
Aditi is praised as a cow in Madhyandin Yajurveda 13.43, during the process of laying of the altar. It is found mentioned as a cow in Rigveda 1.153.3
But Aditi is also mentioned as the universe, in the form of outer space, atmosphere as well as the earth. she is the father as well as the son. Aditi is the five people, the four varnas, and the fifth the Nishad. Those who are already born, and those who are yet to be born, are forms of Aditi only. अदितिर्द्यौरदितिरन्तरिक्षमदितिर्माता स पिता स पुत्रः |
विश्वेदेवाऽ अदितिः पञ्चजनाऽअदितिर्जातमदितिर्जनित्वम् || ( Rigveda 1.89.10, Madhyandin Yajurveda 25.23.)
Shatpath Brahmanam (10.6.5.5) gives etymology of Aditi as :-….. सर्वं वाऽ अत्तीति तददितेरदिदित्वम् सर्वस्यात्ता भवति सर्वमस्यान्नं भवति य एवमेतददितेरदिदित्वम् वेद | That one who eats everything in the world, or for whom all of the universe is the food, is the Aditi.
It also states that Aditi is the earth, the skin that covers all of the earth. Offering is made in the Fire for Aditi. ( 18.104.22.168 अदित्यास्त्वगसि प्रतित्वादितिर्वेत्वितीयं वै पृथिव्यदितिस्तस्या अस्यै त्वग्यदिदमस्यामधि किञ्च……, 22.214.171.124 स यददित्यै चरुं निर्वपति | इयं वै पृथिव्यदितिः सेयं प्रतिष्ठा तदस्यामेवैतत्प्रतिष्ठायां प्रतितिष्ठति तस्माददित्यै चरुं निर्वपति), and the power of speech, the Gods established themselves through the speech form of Aditi. ( अदितिष्टे बिलं गृभ्णात्विति वाग्वाऽअदितिरेतद्वाऽएनां देवाः कृत्वा वाचादित्या निरष्ठापयन्…. 126.96.36.199).
In contrast to the same, Diti, that is mentioned as the sister of Aditi, in the puranas, is not mentioned in the vedas, nor is her progeny of the demons known as “Daityas”, although the demons like Asura and Rakshasa are there in the vedas.
The concept of Diti is purely a work of the puranas, where she is shown as a contrast to Aditi, the mother of the Aditya group of Gods. The later day stories say that both Aditi and Diti were wives of same sage Kashyap, and they produced the Gods and demons. But none of this is of vedic origin. Perhaps the Puranas have developed the concept of Diti, as an alter ego to Aditi, both were conceptualised as sisters, opposite to each other.