I was trying to find out when “prince” developed the implicated normal meaning of “heir apparent”, as someone asked. So this site was of course my first port of call.
But there is a curious sentence on here under “prince”.
“As “heir apparent to a throne,” mid-14c. (Prince of Wales ).”
The title “Prince of Wales” given to the future king Edward II was not to identify him as the heir apparent. It was an existing title given to him, previously held by effectively independent princes of Wales. It no more implies that “prince” means “heir apparent” than “Duke of Cornwall” implies “duke” means “heir apparent”.
(And “Duke of Cornwall” is a title automatically possessed by the heir apparent, whilst “Prince of Wales” is not, meaning “prince” in this context is even further distanced from the concept.)
In the fifteenth century, when Owain Glyndwr took the title “Prince of Wales”, I’m sure you don’t think he was claiming to be anything other than an independent leader, not an “heir apparent”! 
Thus, the mere fact that Prince of Wales was a title which was given to an heir apparent is not implication that “prince” meant “heir apparent”.
That’s a common error, which can create quite some confusion in the minds of English people (in particular) towards Wales, so it isn’t the first time I’ve come across it!
So does this statement in the definition have anything else behind it, other than simply the title happening to have been given to someone who happened to be an heir apparent?
It looks to be possibly a misreading of OED?
Which says - “Originally in Prince of Wales, a title of the deposed Welsh rulers conferred (from the 14th cent. on) upon the eldest surviving son of the King or Queen of England, the epithet prince being later extended to all male children of the reigning British royal family”
This is not saying that “prince” meant “heir to the throne” from the 14th century.
It is saying that the heir to the throne was granted that particular title from the 14th century onwards, and possibly because of this, the word “prince” later acquired additional meaning.
When that extended meaning came to include “heir to the throne” as a general meaning for “prince” is not specified, but it doesn’t seem to have been 14th century.
In the entry here, instead of - [ As “heir apparent to a throne,” mid-14c. (Prince of Wales ). The meaning “king’s son, scion of a royal family” is by mid-15c. ]
I would suggest something along the lines of [The meaning “king’s son, scion of a royal family” is by mid-15c, possibly by extension of the word ‘prince’ from the title “Prince of Wales” conferred on the eldest surviving son of the King or Queen of England from the 14th cent on.]
(But better written!) would be better.
(Assuming 15th century is the correct date here.)