Though it appeared earlier, this word is best remembered because it features in Hamlet, in the scene in which his father’s ghost tells Hamlet of his murder and asks him to avenge it. When Marcellus and Horatio enter, the ghost cries from the cellar below for them to swear that they will never divulge what Hamlet is about to tell them. Hamlet shouts to his father, “Art thou there, truepenny?”.
It was a term of affection, comparing an honest or trustworthy man to a genuine coin. This may strike us today as not being important, when pennies are mere tokens made of base metal, but in Shakespeare’s day, pennies were silver and were comparatively valuable. Counterfeiting was rife.
The word has never been common. Sometimes it appears as a direct quote of Hamlet’s words, as a humorous way of asking “who’s there?” (as in Colin Wilson’s Ritual in the Dark of 1976: “He pulled her shoulders back on to the bed, and kissed her. There was a heavy thump from overhead. Sorme looked at the ceiling, saying: Are you there, truepenny?”).
At one time, attempts were made to derive it from Greek trupanon, a borer, from which we derive the name of the surgical instrument trepan; E Cobham Brewer in early editions of his Dictionary of Phrase and Fable, argued this and commented that it was, “an excellent word to apply to a ghost ‘boring through the cellarage’ to get to the place of purgatory before cock-crow.”