Acinteyya: lit. ‘That which cannot not be thought of’, the unthinkable, unimaginable, inconceivable, incomprehensible, impenetrable, that which transcends the limits of thinking and over which therefore one should not speculate. The 4 unthinkables are: the potential range of a Buddha buddha - visaya, the potential range of the meditative absorptions jhāna - visaya, the potential range of kammic-result kamma - vipāka, and speculation over the world loka - cintā, especially over an absolute first beginning of it, and whether it is infinite in space and time see: A. IV, 77.
Therefore, o Bhikkhus, do not speculate over the world as to whether it is eternal or temporal, limited or endless. Such speculation, O Bhikkhus, is senseless, has nothing to do with genuine pure conduct see: ādibrahmacariyaka-sīla, does neither lead to aversion, detachment, ceasing, nor to peace, not to full comprehension, not to enlightenment or Nibbāna. S. LVI, 41.