American Dictionary of the English Language

FOREFEND', verb transitive

1. To hinder; to fend off; to avert; to prevent approach; to forbid or prohibit.

2. To defend; to guard; to secure.

This word, like the Latin arceo, is applied to the thing assailing, and to the thing assailed. To drive back or resist that which assails, is to hinder its approach, to forbid or avert, and this act defends the thing threatened or assailed.