"I am buying a third-hand book."
Does this mean I am the third or fourth owner of this book after I buy it?
"I am buying a third-hand book."
Does this mean I am the third or fourth owner of this book after I buy it?
1st owner buys new, keeps 1st-hand, sells 2nd-hand. 2nd owner keeps 2nd-hand, sells 3rd-hand. British vehicle logbooks work this way - each owner is referred to as the 'keeper', referred to in conversation by the appropriate preceding ordinal. Information and evidence may be treated similarly in legal, or other rigorous contexts… or gossip, vulgarly?
In practice, most things are described only as 'secondhand' irrespective of the number of previous owners, since the chain of possession is seldom documented. Unless it matters, this usage is certainly the least confusing, if not strictly accurate. 'Pre-owned' is a broadly accurate contrivance. 'Pre-loved' might be cynically regarded as broadly inaccurate, if not deliberately misleading. Any others?
I think 'third-hand' is simply humorous hyperbole, meaning 'so second-hand that it seems like an understatement to merely say second-hand'. Things are second-hand no matter how many owners there are after the first.
third-hand can be taken literally or figuratively.
In the literal sense, it refers to having a third owner, as others have said. In a literal sense, it does not mean having a fourth owner.
In a figurative sense it simply means not the original owner and not the second owner. There might be several reasons why someone would say this.
It might be said to emphasize (in stronger terms than what second hand means):
What a great question!
When you "buy a second-hand car" ("I just bought a second-hand ford") it can indeed mean that you are now (only) the second owner. So it was not really second-hand until the moment you bought it.
The simple fact is, like many things in English, it is a little unclear. the simple fact is the phrase in hand would not absolutely clearly let people understand the situation. That's just how it is with many phrases in English.
In fact I believe I've lterally said this sentence: "That car I have is second-hand, well I mean I'm about the third or fourth owner..."