Second-person singular simple present form of grieve(verb)
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Use "grievest" in a sentence
"This is one of your grievest failures, since you have done nothing to help prevent the corruption and perversion of your fellow republican members."
"Thou lovest, without passion; art jealous, without anxiety; repentest, yet grievest not; art angry, yet serene; changest Thy works, Thy purpose unchanged; receivest again what Thou findest, yet didst never lose; never in need, yet rejoicing in gains; never covetous, yet exacting usury."
"When he saw the letters all edged in black oh he's bound to grievest weeping"