Middle English: from Old French forclos, past participle of forclore, from for- 'out' (from Latin foras 'outside') + clore 'to close'. The original sense was 'bar from escaping', in late Middle English 'shut out', and 'bar from doing something' (sense 2), hence specifically 'bar someone from redeeming a mortgage' (sense 1, early 18th cent.)
