Shūnyam is the formal Sanskrit for Śūnya in common-speak. Etymologically, Shūnyam originate in the notion of hollowness, of ‘Empty Inside’.
The term ‘Empty’ or ‘Null’ as used in English translations of Shūnyam originate directly from the vocabulary of Classical Logic as does the word ‘Form’ as used in the Heart Sutra.
[Although no guru, fee-speaker or book-writer I have met is aware of this root, which might explain their wildly creative interpretations of these two terms.]
Shūnyam itself is not to be confounded with the numerous versions of Śūnya with a suffix that evolved in the regional Dharmic literatures well into the 10th Century [ŚūnyaBrahman, ŚūnyaPurusha et al]. Or the selective use of the term ‘Emptiness’ in others [Kashmiri Shaivism, the Southern Bhairava et al]
Nor with the various versions of Shūnyathā, from the early Theravada [Pali: Suññatā] to the Heart Sūtra of the Madhyamaka.
The expression Shūnyathā is a later derivative construct to Shūnyam and most likely found its inspiration in another much earlier term Táthātā, itself a construct that mounted on the original term Tát.
Shūnyam is to Shūnyathā as Tát is to Táthātā. Shūnyam and Tát carry the original insights; Shūnyathā and Táthātā were later constructs meant as pedagogic tools that in time took on a life of their own repeatedly invading the space of the original expressions themselves [thanks to book-read scholars.]
Without getting into the details here, the extensions still depend on late-stage binary divides; the original terms do not.
Instead of converging on ‘True Nothing’, the doctrine of Shūnyathā limits to a late-stage divide of ‘Emptiness: Form’ in exact parallel to the Vedanthic stop at ‘Being: Consciousness’. As in the Metaphor of the Raft, all divides are left behind in a converging to Shūnyam. [I’ll elaborate on this at some later Post for the interested reader.]
As an aside, the most consistent definition for Shūnyathā in the higher texts has been ShūnyathāShūnyathā: ‘The Emptiness of Emptiness itself’. Yes, a full-blown Self-Eating Expression.