A nice summary of the various suggestions for the word pāṭimokkha can be found here:
I want to focus on just one element. I’m going to quote the relevant portion of Nyanatusita’s introduction. This is slightly different than the one posted above, but it arranges the material more conveniently:
[I.B. Horner] quotes the Pali English Dictionary, according to which pātimokkha is said to have the same meaning as paṭimokkha at J V 25: “that promise to be obliged has not been released” (taṃ saṅgaraṃ paṭimokkhaṃ na muttaṃ). A few other references also support the future passive participle etymology: J V 166: Yaṃ (bandhanaṃ) natthuto paṭimokkh’assa pāse: “(the bondage) which was tied through his nose (of the nāga) in a noose” and D I 12 & 181: osadhīnaṃ paṭimokkho: “the binding on of medicinal herbs” or, in accordance with the commentarial explanation of this, “removal of/releasing from [caustic] medicinal herbs.”
Zeroing in on the examples given, in the MS edition we have:
ja513:6.2: Taṁ saṅgaraṁ paṭimukkaṁ na muttaṁ
ja524:10.2: Yaṁ natthuto paṭimokkassa pāse
These clearly mean “binding”. Note that the spelling of the two words is different, and it also differs from the examples cited by Nyanatusita, presumably from the PTS editions. The most striking variation is the loss of the aspirate -h, but none of the changes affect the etymology, only the inferred grammatical form.
There is also:
dn1:1.27.2: osadhīnaṁ paṭimokkho
The latter appears thrice with ṭ and once with t. Again the spelling variants, though relevant to the argument, are not noted. Here the meaning is not as clear, but I think the sense “binding on of herbs” is much simpler and more obvious that the commentary’s explanation (which seems to me backformed from their explanation of the pāṭimokkha itself). It is a common procedure in traditional medicines to apply herbal salves and the like locally by binding them on with a bandage to the affected area; I have had this done to reduce knee swelling.
Missing is the following in the Thera-apadāna:
tha-ap25:5.3: Tena kammena sukatena,
tha-ap25:5.4: paṭimokkhāmi duggatiṁ
By means of that well-done deed
I am freed from bad rebirth.
Here the PTS reads parimokkhāmi, which is perhaps why it has been overlooked. But it cites paṭimukkhāmi as a Sinhalese variant, and since both MS and BJT have paṭimokkhāmi it is fairly well attested. The sense is clearly “release”, regardless of the chosen reading.
So far we have shown that:
- there is a fair deal of variation in the relevant readings
- the examples cited by Nyanatusita do not exhaust the Pali
- there are clear attestations of the sense “binding” and less clear attestation of “release”.
Most interestingly, there is variation in the forms with and without aspirate. Why is this interesting? Because the form paṭimukka is well-attested in early Pali in the sense “binding”. It commonly occurs in contexts such as paṭimukkassa mārapāso, “caught in Māra’s trap”. Despite the lacking aspirate, it is from the same root as pāṭimokkha, or at least as the most obvious root, from muñc “free”, with the prefix paṭi creating an antonym.
- (The variation in the aspirate can be explained by the Sanskrit form mokṣ. It is common linguistically for Sanskrit sibilants to weaken into aspirants in Pali. Compare Sanskrit skandha with Pali khandha.)
The two words have a straightforward relationship.
- paṭimukka is “bound”, past participle with adjectival sense.
- pāṭimokkha is “(that which is) binding”, “obligation”, future passive participle (“gerundive”), with the implicit affix -ya and a lengthened initial vowel after the style of, eg. pāṭidesaniya.
The Compendious Grammar notes of this affix:
This is called a kicca affix but is included in the kita chapter of Kaccāyana (Kacc 545) – an affix of the future passive participle (Kacc 540).
Kaccāyana lists pāṭimokkha under the taddhita constructions where the initial vowel is lengthened, which argues against certain of the commentarial readings, and supports ours. (As usual, spelling is not standardized: VRI edition has ṭ, while the excellent and super-helpful translation by Ashin Thitzana reads t.)
Despite the fact that the spelling with a dental t (pāti) is most prevalent in modern editions, I think this is probably due to normalization in line with the commentary. Elsewhere the prefix is usually spelled paṭi, and I see no reason why this should change with the lengthening of the initial vowel; again, cp. pāṭidesaniya.
In conclusion:
- derivation is paṭi + muñc + ya
- sense is “(that which is) binding”, “obligation”
- spelling is pāṭimokkha