An old joke I found in Mark Forsyth's "The Etymologicon", originally mentioned in the OED
A country lad, having been reproved for calling persons by their Christian names, being sent by his master to borrow a dictionary, thought to show his breeding by asking for a Richard Snary.
I understand the joke (for those who don't, the boy misheard Dictionary as Dick Snary, thinking it's a man's name.
Ignoring the outdated pronunciation needed for the joke to work, the confusion only works with "borrow a dictionary" and "borrow a Dick Snary"
It doesn't work in modern English, "get a dictionary" and "get Dick Snary" doesn't quite have the same effect.
But what does this old-fashioned article "a" before a person's name mean?