Adjectives

(s)severe, terrible, wickedintensely or extremely bad or unpleasant in degree or quality“severe pain”, “a severe case of flu”, “a terrible cough”, “under wicked fire from the enemy's guns”, “a wicked cough”
(s)hard, knockout, severevery strong or vigorous“a hard left to the chin”, “a knockout punch”, “a severe blow”
(s)austere, severe, stark, sternseverely simple“a stark interior”
(s)severe, spartanunsparing and uncompromising in discipline or judgment“a parent severe to the pitch of hostility” (H.G.Wells), “a hefty six-footer with a rather severe mien”, “a strict disciplinarian”, “a Spartan upbringing”
(s)dangerous, grave, grievous, serious, severe, life-threateningcausing fear or anxiety by threatening great harm“a dangerous operation”, “a grave situation”, “a grave illness”, “grievous bodily harm”, “a serious wound”, “a serious turn of events”, “a severe case of pneumonia”, “a life-threatening disease”
(s)severevery bad in degree or extent“a severe worldwide depression”, “the house suffered severe damage”