The Chambers Dictionary says usable.

System usability scale was created in 1986.

Usability Professionals' Association was created in 1991.

"Usability is a term used to denote the ease with which people can employ a particular tool or other human-made object in order to achieve a particular goal. Usability can also refer to the methods of measuring usability and the study of the principles behind an object's perceived efficiency or elegance."

The author of 'Prioritizing Web Usability' is Jakob Nielsen. Nielsen, a usability consultant, was born in Copenhagen, Denmark in 1957. He holds a Ph. D. in human-computer interaction.