A variant spelling or archaic form of 'forestallment'; prevention or obstruction.
From 'forestal' (an older spelling/form) + '-ment.' This appears to be an obsolete variant of 'forestallment,' possibly from dialectal or Middle English usage.
This word is so archaic it barely exists in modern English—it's the kind of thing found in old legal documents where spellings were way more fluid and variant forms coexisted.
Complete word intelligence in one call. Free tier — 50 lookups/day.