testate
Concise Oxford English Dictionary © 2008 Oxford University Press:
testate /ˈtɛsteɪt/
▶adjective having made a valid will before one dies. ▶noun a person who dies testate.
– origin ME: from L. testatus ‘testified, witnessed’, past part. of testari, from testis ‘a witness’.
'testate' also found in these Oxford entries:

