Word for a false definition used for comedic effect

I think both of your examples are homophonic puns because the joke comes from the how part or all of a word sounds similar to another word, and the words are not synonyms.

It isn't a single word answer, but the process has a whole dictionary devoted to it called the Uxbridge English Dictionary which is also a game in the spoof BBC Radio 4 panel show I'm Sorry I Haven't a Clue.

Two definitions picked randomly from an online version (link here):

• Handicap. A very convenient hat
• Hijack. A young man under the influence of narcotics

And, of course, the dictionary is available on amazon.

Perhaps we should coin the new term "Uxbridge-ing".

They're sometimes called daffynitions, although that word makes me grind my teeth when I hear it. The inverse, by the way, is called a sniglet.