In message , thoss
writes

On Wed, 28 Jun 2006 Paul Terry wrote:

thus Kinges became King's and childes became child's. And from this
the apostrophe-s ('s) came to be used for the genitive (possessive)
form of most nouns, thus representing the spoken form of the language
more faithfully than the Old English form.

I always thought it was from omitting hi in King his, leading to King's.

That has long been used as a simple explanation in teaching of what the
genitive case *can* indicate, but it is not rooted in historical fact.

For instance, Queen's College is rather unlikely to be the modern form
of "Queen his college"

As I said above, the apostrophe simply indicates the omission of the
final e from the Old English genitive ending, -es.

Thus, King's College is the modern form of Kinges College.
And Queen's College is the modern form of Queenes College.

And, although the apostrophe can now be used to differentiate between
the genitive singular and the genitive plural (Queen's College Oxford v.
Queens' College Cambridge, mentioned earlier), this is a relatively
modern usage - the Cambridge College was known as Queenes and then
Queen's until 1831 (when historicism and affectation combined to move
the apostrophe along one letter
--
Paul Terry