harshly uninviting or formidable in manner or appearance; "a dour, self-sacrificing life"; "a forbidding scowl"; "a grim man loving duty more than humanity"; "undoubtedly the grimmest part of him was his iron claw"- J.M.Barrie

threatening or foreshadowing evil or tragic developments; "a baleful look"; "forbidding thunderclouds"; "his tone became menacing"; "ominous rumblings of discontent"; "sinister storm clouds"; "a sinister smile"; "his threatening behavior"; "ugly black clouds"; "the situation became ugly"

Repelling approach; repulsive; raising abhorrence, aversion, or dislike; disagreeable; prohibiting or interdicting; as, a forbidding aspect; a forbidding formality; a forbidding air.

an official prohibition or edict against something