"gravest" in the adjective sense
1. grave, sedate, sober, solemn
dignified and somber in manner or character and committed to keeping promises
"a grave God-fearing man"
"a quiet sedate nature"
"as sober as a judge"
"a solemn promise"
"the judge was solemn as he pronounced sentence"
2. dangerous, grave, grievous, serious, severe, life-threatening
causing 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"
3. grave, grievous, heavy, weighty
of great gravity or crucial import requiring serious thought
"grave responsibilities"
"faced a grave decision in a time of crisis"
"a grievous fault"
"heavy matters of state"
"the weighty matters to be discussed at the peace conference"
Source: WordNet® (An amazing lexical database of English)
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