The word pātimokkha is variously explained, the oldest explanation being that the observance of the rules is the face (mukhaṃ), the chief (pamukhaṃ) of good qualities.
Source: SuttaCentral
with Childers plausibly as paṭi + mokkha, grd. of muc (Caus. mokṣ˚) with lengthening of paṭi as in other grd. like pāṭidesaniya.
Thus in reality the same as paṭimokkha 2 in sense of binding, obligatory obligation, cp. Ja.v.25. The spelling is freq. pāti (BB pāṭi˚).
The Sk. prāṭimokṣa is a wrong adaptation fr. P. pātimokkha, it should really be pratimokṣya “that which should be made binding.”
An expln of the word after the style of a popular etym. is to be found at Vism.16
Source: SuttaCentral
Would anyone be kind to check what is found in Vism.16 ?