I have heard there are 4 unthinkable (acinteyya) concepts in Buddhism. Not Acintya.
The four imponderables are identified in the Acintita Sutta, Anguttara Nikaya 4.77, as follows:
- The Buddha-range of the Buddhas [i.e., the range of powers a Buddha develops as a result of becoming a Buddha];
- The jhana-range of one absorbed in jhana [i.e., the range of powers that one may obtain while absorbed in jhana];
- The [precise working out of the] results of kamma;
- Speculation about [the origin, etc., of] the cosmos is an imponderable that is not to be speculated about.
Why It says Unthinkable?