Superlative form of discreet: most discreet.(adjective)
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Use "discreetest" in a sentence
"Humour and Inclinations, before he gave himself irrevocably to me, it oblig'd me to regulate my Behaviour with the discreetest Precautions my poor unexperienc'd Thoughts could dictate."
"And thus did Lycurgus, for chastisement of his fault, make of a wild and passionate young man one of the discreetest citizens of"
"He is the prettiest, discreetest fellow that ever my eyes beheld, or that ever dipped pen into ink."