intense, extreme, or devastating (often describing pain, weather, or an effect)

severe; strict; stern; harsh (usually referring to an attitude, criticism, or punishment)

forceful and intense, especially in look, style, or manner

in a stern voice

to continue the struggle; to persist with unremitting efforts, especially after a success or to reach a higher goal

mournful (sound)

to become more intense or severe, typically used in a negative context such as a shortcoming, bad habit, or unfavorable situation

pass like thunder and move like the wind (idiom); swift and decisive reaction

to practice strict economy

malicious spirit; devil

to do something with rigor; to carry out or enforce strictly

appearing fierce or strong on the outside while being weak or cowardly at heart; a sheep in wolf's clothing

solemn in countenance; strict and unsmiling

solemn in word and countenance; strict and unsmiling

stern and harsh in attitude, expression, or manner; pitiless or merciless

possessing a majestic and stern presence that commands respect and fear

frenzied and violent

harsh, coarse, or severe in character, interpersonal manner, or physical texture

severe in both looks and speech

to give someone a stern look; to glare at someone

to strike a severe blow, crack down on, or take strong measures against illegal activities, crime, or social misconduct

stern; unsympathetic; icy

although I don't understand it, it seems pretty awesome (Internet slang)

to be full of vigor

to criticize someone or something harshly and strictly; to slate

shrill (of a voice or sound)