The site of Etymonline tells that the word ‘dub’ comes from “give a name to,” originally “make a knight,” from late Old English dubbian "knight by…
As I am Dutch, I was wondering if the word ‘dub’ could also have references to the Dutch word ‘doop’ ( [doop - WikiWoordenboek) and the Danish word ‘dåb’ (dåb — Den Danske Ordbog), which both mean ‘to baptise’. With baptising often additinal names are given and there is a kind of inaugurational ceremony.
Etymonline only shows where modern English gets the word from. That means words in other languages can easily be related (or even be the same word!) while at the same time not belonging in Etymonline (if English got the word from somewhere else instead).
To me it looks like you’re probably right that these could be related somehow. English also has “daub”, which sounds almost the same as “dåb”, and may be related to them too.
Since the word does have some uncertainty about the origin, this isn’t a bad suggestion if anything can actually be found to back up a connection.
It’s in English from circa 1085 (the chronicle with the word is reprinted here) and certainly there means bestowing of knighthood, though what process was used isn’t clear.
The Dutch etymological site suggests the Dutch doop is cognate with English deep.
Yes I also thought about “to dip” might be cognate.