In his seminar on “The Purloined Letter” Lacan mentions two acts of theft in Poe’s story:
1) Early in the story, the Minister steals the Queen’s letter by replacing it with a fake letter.
2) Later, Dupin steals the letter back from the Minister by replacing it with another piece of paper.
In both events, there is an authentic letter that is stolen by the agent and a fake letter that is planted in its place. Let us coin a new term ‘latcher’ and name these two objects as follows: The purloined letter and the latcher that is planted in its place.
A letter lets you read it , it’s legible, one can reveal its secret by publicly available means. Its function is clear: If revealed to the public eye (or the King’s eye), the letter “would bring in question the honor of” the Queen.
In contrast, a latcher latches the linguistic entrance, it’s illegible and opaque, it bars meaning and requires contextual interpretation or translation. It has a mysterious quality that latches on its addressee and demands him/her to latch onto its secret. This is obvious for the second latcher planted by Dupin since it explicitly bears an enigmatic note that compares the two thieves (Minister and Dupin) to two mythological figures (Thyestes and Atreus). But the first latcher planted by the Minister is no less enigmatic and captivating, since it direly frightens the Queen precisely because its presence implicitly evokes the Minister’s unknown malicious intentions. The Prefect fails and Dupin succeeds precisely in deciphering this unknown intention and desire invoked by the first latcher.
In Enjoy Your Symptom! (1992) Slavoj Žižek provides multiple interpretations for Lacan’s maxim that a letter always arrives at its destination. In the imaginary sense, a letter arrives at its destination because it interpellates its addressee into an ideology. In the symbolic sense, a letter arrives at its destination because it evokes an unpaid symbolic debt. Finally he says the following about the real sense of the letter’s arrival:
The ultimate variation on the theme of a letter that always arrives at its destination reads therefore: “you can never get rid of the stain of enjoyment” – the very gesture of renouncing enjoyment produces inevitably a surplus enjoyment that Lacan writes down as the “object small a.”
This opaque stain of enjoyment is precisely the barring and captivating latcher that is planted in place of the purloined letter. In contrast to the imaginary letter and the symbolic letter both of which can be said to originate from a ‘home’ or a ‘homeland’ (e.g. being interpellated by national ideology and being called to sacrifice due to your moral debt) the real letter is a latcher that originates from the symptom (not the sint-‘home’ ).
 To be sure, ‘letter’ has no etymological connection to ‘letting’, but this does not stop us from associating them.