issi SUFFIX
-est, most ~, much ~, makes SUPER;
expertissi.mo ADJ 0 0 DAT S M SUPER
expertissi.mo ADJ 0 0 DAT S N SUPER
expertissi.mo ADJ 0 0 ABL S M SUPER
expertissi.mo ADJ 0 0 ABL S N SUPER
expers, (gen.), expertis ADJ [XXXDX] lesser
free from (w/GEN); without; lacking experience; immune from;
expertus, experta, expertum ADJ [XXXEO] uncommon
well-proved, tested; shown to be true;
issi SUFFIX
makes a verb PERF PPL into an adjective SUPER (amat.issimus => most/much loved)
expertissi.mo ADJ 0 0 DAT S M SUPER
expertissi.mo ADJ 0 0 DAT S N SUPER
expertissi.mo ADJ 0 0 ABL S M SUPER
expertissi.mo ADJ 0 0 ABL S N SUPER
experior, experiri, expertus sum V (4th) DEP [XXXDX] lesser
test, put to the test; find out; attempt, try; prove, experience;

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.