Bound or fastened with chains; imprisoned or restricted by chains.
From the prefix 'be-' plus 'chained' (from Old French 'chaine,' from Latin 'catena'); the prefix adds emphasis to the state of being chained.
The 'be-' prefix in Old English was used to intensify verbs, making 'bechained' sound more dramatically imprisoned than just 'chained'—it's the linguistic equivalent of exclamation points.
Complete word intelligence in one call. Free tier — 50 lookups/day.