The story
- Proto-Indo-European*upó
- Proto-Italic*supo
- Latinsub
- Latinsub-
- Proto-Indo-European*bʰer-
- Proto-Indo-European*bʰéreti
- Proto-Italic*ferō
- Latinferō
- Latinsuffero
- Latinsufferre
- Vulgar Latin*sufferīre
- Old Frenchsuffrir
- Middle Englishsuffren
- Englishsuffer
- English todaysuffering
By surface analysis, suffer + -ing. Mostly displaced English bale (“suffering, woe, torment”) and English woe.
Etymology from Wiktionary, CC BY-SA 4.0.