Deify is only one letter ahead of defy and good one letter ahead of god. Devil one letter ahead of evil and what else can there be in this field.(?)

A conundrum:

What pair of words changes its number and gender by the addition/deletion of a single letter?

Ja hallo,I do not mean just any words. I mean words that sort of cling together like evil-devil and good-god and the I defy-deifying or vice versa.( please define "ahead" better as I wasn't English remember) And what is a conondrum if you please?

Merriam/Webster on "Conundrum" -

Definition of CONUNDRUM

1
: a riddle whose answer is or involves a pun
2
a : a question or problem having only a conjectural answer
b : an intricate and difficult problem
Examples of CONUNDRUM

The conundrum of how ancient peoples were able to build such
massive structures, i.e. pyramids,without the benefit of today's
knowledge and technology. A riddle to us in the 21st century.

..or, if you prefer, just any old puzzle. I think mine comes pretty close to your meaning, too, actually.

re ahead: "ahead" usually has to do with position in space, literal or figurative (one runner is ahead of another, or a team is ahead in the score) but often implies that the front is better than the back. With evil/devil and good/God the betterness isn't there, and with defy/deify there is contrast but no statement of preference, so it's arbitrary which is "better." That was the source of my objection quibble.

Thank you, now I really have a puzzle to solve.
Thank you Luke, I'm so disappointed my grammar still has these little setbacks.

I wish I could do as well as you in any language other than
English. European folks are so lucky with the opportunity
to learn so many more. Met some 12 year olds in Wales once
and the three of them all spoke five languages. Astounding.
All ours can deal with is textspeak in so many circumstances.

OK, what's the other one of the pair with conundrum

The second pair the shorter word is plural and the longer word adds an s and is singular.

LOT SLOT
- Both are prolly an object or objects.

what about

Mrs and Mr

I hope you did not miss the big ugly laugh I ended my post with...

I've not ever paid much attention to smileys, ever since a
huge retailer here used it ad nauseam, and it drove me to
distraction in advertising which I don't appreciate to begin
with. So I guess I missed it.

Spoiler alert

PRINCES / PRINCESS

Indeed.