Well — I must say that I don't have much interest about that.
If there is something, I wouldn't be able to put a name on it. Would I?
Sāṃkhya (aka sāṅkhya) would call it Purusha. With the latter being the seer.
Purusha is a totally distinct principle - it is distinct fom Prakriti (Nature).
Pre, contemporary, and Post-Buddhist Vedism is a bit trickier, because there is not just one clear representation.
To make it simple (but not accurate), Purusha would be the Unborn and without breath (nir vā) — the purusha in the self (atma) of a human is Brahma. And the light of Purusha is a subdued atma.
Also, by contemplation, brahma expands (citaye).
(Tapas comes from two roots — it means either contemplation, or austerity.)
Here the ci is what expands the world.
None of these philosopies meet Buddha standard.
In Sāṃkhya, Purusha is the seer.
Buddhi (aka Mahat) is the first evolvent to be produced by the primeval Prakriti, at the contact of Purusha.
I would equate Prakriti to the ci. But it's a bit more complicated than that.
However, you cannot liken this kind of ci, with the Buddhist ci - that is responsible for both the development (evolvement) and the seeing (seer).
In pre, contemporary, and Post-Buddhist Vedism, the ci is more involved with the self (atma). And we know that Buddha rejected such a self/self in paṭiccasamuppāda.
So what is this Abyākata (undeclared) you seem to be refering to - that seems to look like Purusha, or the Unborn, or Nibbāna (nir vā - free from breath (blowing))?
Well - it seems that we can't even call them that way - and definitely cannot define them.
Instead, what the Buddha propounded as a means, was to understand as they have come to be, the origin and passing away of the six fields of sensory experience (of contact), their satisfaction, unsatisfactoriness, and the escape from them (viz. total unapropriation as "mine", then "I"); as well as the stilling of all saṅkhārā— that is to say how to reach nibbāna (without remnant).
Definitely it does not mean to understand the nature of the abyākata (avyākata). Does it?