Q. Joshua’s father’s name is “Nun”. What does it mean?
A. It actually means a fish, from a root that means to sprout or flourish (e.g. Psalm 72:17).
Nun is also the 14th letter of the aleph-bet; the original shape of the letter was like a fish with a tail. Another word from the same root is nin, progeny (e.g. Gen. 21:23).
It is also possible that bin-nun means a disciple; Joshua was of course the leading disciple of Moses.
There are a number of Biblical references to Joshua as the son of Nun, though Joshua himself was originally Hoshea (Num. 13:8, 16).
In I Chron. 7, we not only learn that Nun was the father of Joshua but he himself was the son of Elishama, a prince from the tribe of Ephraim. (It may be only a coincidence, but Ephraim also comes from a Hebrew root that means to be fruitful).
Why Elishama named his son Nun probably has nothing to do with the idea of a fish. It is more likely to be a prayer that though Nun the tribe would be blessed with posterity.