How to analysis this vocabulary?
Pac(a/i) + [ṃ of abbhāsa(root-repeating)] + pac(a/i) + a = papañca (saddanīti dhātumālā).
Pāka/vipāka, which use the same pac(a/i)-root, didn't abbhāsa by Buddha, because it is resultant. It is not the lead-cause dependent-origination-loop's repeating. So, Buddha didn't abbhāsa it.
What does pac(a/i) of papañca mean?
It refers to kilesa-vatta (unwholesome-causes) of the dependent origination which are the causes of the dependent-origination-loop's repeating. Because Kamma-vatta (formation/kamma-becomming) depending on kilesa-vatta (avijjā/taṅhā/upādāna) to cook(pacati) pāka/vipāka (resultants) of the dependent origination (vaṭṭa/paṭiccasamuppāda).
Why Buddha did abbhāsa(root-repeating) to pac(a/i) as papañca?
To refer papañca to kilesa-vatta (unwholesome-causes) of the dependent origination. I described above.
Where are kilesa-vaṭṭa (formation) in dependent origination?
The italic text below of Saṃ. Nidāna. Vibhaṅgasutta are kilesa-vaṭṭa (formation), the bold text are vipāka-vaṭṭa, the regular text are kamma-vaṭṭa:
– Katamo ca, bhikkhave, paṭiccasamuppādo?
– And what, bhikkhus, is paṭicca-samuppāda?
Avijjā·paccayā, bhikkhave, saṅkhārā;
Conditioned by avijjā, bhikkhus, there are saṅkhāras
conditioned by saṅkhāras, there is viññāṇa
conditioned by viññāṇa, there is nāmarūpa
conditioned by nāmarūpa, there are saḷāyatanas
conditioned by saḷāyatanas, there is phassa
conditioned by phassa, there is vedanā
conditioned by vedanā, there is taṇhā
conditioned by taṇhā, there is upādāna
conditioned by upādāna, there is bhava
conditioned by bhava, there is jāti
jāti·paccayā jarā-maraṇaṃ soka parideva dukkha domanass·upāyāsā sambhavanti. Evam·etassa kevalassa dukkha'k'khandhassa samudayo hoti.
conditioned by jāti arise jarā-maraṇa, sorrow, lamentation, dukkha, domanassa and distress. Thus arises this whole mass of dukkha.
Which are the evidence sutta of this answer?
Every sutta which are contented papañca and papañceti are the evidences. They talking about dependent origination (paṭiccasamuppāda). So, I analysis papañca-word as dependent origination follow to those suttas' context.
Why atthakathā comments papañca as the Resistance?
Because the kilesa-vaṭṭa causes the repeating of dependent-origination-loop. So, atthakathā comments papañca as the resistance of the dependent-origination-loop cessation.
Why atthakathā comments papañca as only Taṇhā, Diṭṭhi, and Māna, but the sutta refer to 7 anusaya?
It is just a brief of those 7 anusaya to cover 10 fetters in brief 3 kilesa, some point of atthakathā comment more than 3 as well. So, the sutta and atthakathā similarly explained papañca.