Simple past tense and past participle of possess.(verb)
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Use "possest" in a sentence
"Gentlemen, these were a part of the thoughts that then possest me, and I there made a conversion of a piece of an old Ketch, and added more to it, fitting them to be sung by us Anglers: Come,"
"As I thus sate, these and other sighs had so fully possest my soul, that I thought as the Poet has happily exprest it:"
"These were the thoughts that then possest the undisturbed mind of Sir Henry Wotton."