cert.is N 2 2 LOC P N
cert.is N 2 2 DAT P N
cert.is N 2 2 ABL P N
certum, certi N (2nd) N [XXXBO]
that which is fixed/regular/definite/specified/certain/fact/reliable/settled;
cert.is ADJ 1 1 DAT P X POS
cert.is ADJ 1 1 ABL P X POS
certus, certa -um, certior -or -us, certissimus -a -um ADJ [XXXAO]
fixed, settled, firm; certain; trusty/reliable; sure; resolved, determined;

Credits:
This, our local install of the popular standby Whitaker's Words, is possible thanks to the resurrection of the venerable project at William Whitaker's Words, where you will also find extensive documentation. The corresponding GitHub repository is where you can submit issues about missing forms and analyses.
This web interface by Walter M. Shandruk.