This hapax is questionable, and two alternative readings present themselves. Firstly, the word may be the result of a superfluous or misinterpreted er abbreviation symbol, and needs to be corrected to prison(er)ez, i.e. the past participle of the verb prisoner1. Secondly, the word may be a noun rather than an adjective, and thus the plural of the noun prisoner2 (with a voiced -ez suffix instead of -es).