To cause someone or something to lose credibility, reputation, or trustworthiness; to discredit.
From dis- + accredit (from medieval Latin accreditare, 'to trust'). The word 'accredit' meant to give official recognition; dis- reverses this to remove credibility.
This is essentially a synonym for 'discredit,' showing how English sometimes has multiple ways to say the same thing—perhaps 'disaccredit' was preferred in certain time periods or regions.
Complete word intelligence in one call. Free tier — 50 lookups/day.