Alarming
Part of speech: adjective
Definition: causing apprehension, fear or alarm; frightening
Part of speech: verb
Definition: To call to arms for defense
Example sentence: We're losing biodiversity globally at an alarming rate, and we need a cornucopia of different plants and animals, for the planet's health and our own.
Redoubtable
Part of speech: adjective
Definition: Eliciting respect or fear; imposing; awe-inspiring.