Sentence:  For example , when the film is only four minutes old , Neitzbohr refers to a small , Victorian piano stool as `` Wilhelmina '' , and we are thereupon subjected to a flashback that informs us that this very piano stool was <WSD>once</WSD> used by an epileptic governess whose name , of course , was Doris ( the English equivalent , when passed through middle Gaelic derivations , of Wilhelmina ) . 
Meaning of the word marked with <WSD> tags:  at a previous time;