A person who jointly makes a will or testament alongside another person; a cowitness to a legal testamentary document.
Prefix 'co-' (Latin 'cum') + 'testator' (from Latin 'testator' meaning 'one who makes a will', from 'testari' meaning 'to bear witness'). Legal term from modern English.
The word 'testator' literally means 'witness' in Latin because making a will was originally about calling witnesses to vouch that you were of sound mind when deciding who gets your stuff!
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