Really? I’ve never encountered the second one, and can’t find it in the dictionary.
My pet peeves (plural of peef?), as commonly used in newspaper articles by writers who ought to know better:
stanch vs. staunch
stanch v.t., to block the flow of a liquid (or, more loosely, of anything else that can be said to “flow”): Use a tourniquet to stanch the bleeding; sell off an imploding stock to stanch the losses.
staunch, adj., steadfast, unwavering: Staunch allies in the Cold War.
Me either. Is it an archaic usage?
Too and Two. Always getting mixed up.
For example I say "When I got married my wife was 30 and I was thirty - too. Which sounds like I was age 32 when I was really 30. I should say I was “thirty also”.
Sucker and lollipop.
Both describe the same kind of candy but lollipop sounds more fancy than sucker.
Or an overhearing of someone who should be saying ‘slice’?
Unfortunately, “may not” is ambiguous. That is, it may or may not mean what you say it does. 
That caused a lot of confusion in early internet specs, so they formalized the language: you’re supposed to use “MUST NOT” or “MIGHT NOT” (in caps!)
No kidding, though I’d spell that pronunciation as “kashay”.
Advice - noun - to give guidance.
Advise - verb - the act of giving advice.
Councilor: member of a council
Counselor: one who gives counsel
Or maybe someone once got tongue-tied, and came up with “splice” as a portmanteau of “split” and “slice,” which became an inside joke somewhere, and the poster is a late-comer, who didn’t realize it was a joke.
Oh-- wait, I know. Sometimes in splicing branches of trees, when they cut the piece from the bigger tree to splice onto a root to create an artificial sapling (or for a couple of other uses, like bark repair on old growth trees), they refer to it as “cutting a splice.” It’s shorthand for “Cutting off a piece to use for a splice.”
Maybe that’s what the OP is talking about.
I’ve spliced wires, and never heard the term used in reference to wires, but when splices are used in ropes or fabric, the may say “cut a splice” as well, to refer to the piece they are going to use for the splice, if it’s being used to bridge a gap.
Diffuse: to disperse matter within a medium.
Defuse: to ameliorate interpersonal or diplomatic tension in a situation, with the purpose of avoiding a metaphorical explosion.
1000X this.
Sherbet: a type of frozen dessert
Sherbert: a homophone for the phrase Ernie uses to signal his intention to comply with his roommare’s request.
Flammable: combustible; easily set on fire.
Inflammable: combustible; easily set on fire.
What a country!
Proscribe and prescribe are almost opposite in meaning (“proscribe” means “forbid”).
And then there are all those people that give me the heebie-jeebies by using “ect.”. Unless you are referring to a certain medical procedure sometimes used to resolve severe psychiatric symptoms, the abbreviation is “etc.”. If you pronounce it correctly (et cetera) you will be much more likely to spell it correctly.
Espresso: cures my headaches when consumed
**Expresso: **gives me headaches when spoken
Disperse: to spread through the air, as in a gas, or to clear an area of people (“disperse the crowd”).
Disburse: to pay out. It’s literally “dis-purse,” with the consonant “p” voiced. In medieval Latin, “bursa” was a repository for money, and we get the word “purse” as well as “bursar” from it.
taught: provided instructions
taut: tight
oh, and that reminds me:
straight: in an unbending line (walk a straight line)
strait: tight (strait-laced, strait-jacket)