possessives - What does "day's" mean?

I understand what the sentence The house is a full day’s journey from here means, but I’m wondering what day’s is short for in this expression. It doesn’t match any pattern I know.

A couple of examples:

• He’s = he is


• Let’s = let us


• Mary’s car = the car belongs to Mary


• Day’s = it sounds to me like something belongs to a day and this is what I don’t understand. Shouldn’t it be The house is a full day of journey from here instead?

Answer

The fourth example is the correct interpretation of day's, but with two things to keep in mind.

First, in your conclusion you flipped the words around incorrectly*; the journey "belongs to" the day, not the other way around. You could re-write the sentence as:

The house is a journey of a full day from here.

Second, while the journey is "of a day," this does not necessarily mean the day "owns" or "possesses" the journey; grammatically, time periods are simply treated as possessive.

* "A full day of journey" would actually work, but that would make "of journey" a subordinate clause rather than the day belonging to the journey; though, as WS2 brought out in the comments, this should actually be "A full day of journeying".