/ ˈkaʊntəsaɪn; NAmE -tərs-/ verb
[ vn ] ( technical ) to sign a document that has already been signed by another person, especially in order to show that it is valid
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WORD ORIGIN
late 16th cent. (as a noun): from French contresigner (verb), contresigne (noun), from Italian contrassegno , based on Latin signum sign.