I have already mentioned stolid and solid; how about
kudu: antelope
kudzu: vine
And indeed “grizzly” as in bear. Or “grizzled/grizzly” as in a whimpering toddler.
Kudu is also a type of gourd/squash with large leaves. It’s often grown over a pergola to provide shade as well as food, and immigrants from South Asia keep up the custom in my part of London. A photo I posted on another site of a market stall advertising kudu plants caused some conniptions among US-based members!
I’ve seen a spellchecker confuse “Catholic” and “Cthulhu”.
Which led immediately to “does the spellchecker know something we don’t?” jokes.
monorchism: one testicle
monarchism: rule by a single head of state
Monomonarchism: rule by a single head of state with one testicle.
Perhaps “monorchmonarchism”? 
Monoecious; plants with flowers of both sexes on a single plant.
Contrasted with;
Dioecious; plants with flowers of only one sex on each plant, requiring cross-pollination with a different plant.
I always get those two confused. Is it mono- because they are both on one plant, or di- because there are two different plants neccesary? Aggh.
Could be worse. A “haploid” cell has one set of chromosomes, because that’s half the usual number. A “diploid” (or “triploid”, or “quadruploid”…) cell has two (or three or four…) sets of chromosomes.
But you’d think that there’d be something between “half” and “two”. What would a monoploid cell be?
I just learned these words from you. Maybe it’s a sign of my perverted mind, but I immediately thought. “Mono’s can productively play with themselves. It takes just 1 to tango.” Maybe that’ll be mnemonic enough for you. 
Anything where 2 is the usual quantity raises that issue.
Funny but I was dealing with that exact issue at Amazon yesterday. I was buying a product that comes from the factory in a package of 2 identical items. Which Amazon then bundles into offering 1 or 2 or 3 of those 2-packs. But their terminology was inconsistent between the descriptive text and the ordering options. When you order quantity “2”, are you ordering 2 items = one package, or 4 items = 2 packages of 2? By looking at the 3-pack option, which had to be 3 packs of 2 since the items can’t be had singly at all, I concluded that “1 (pack of 1)” had to really mean “1 bundle of one package of 2 items”. Gaah!
Further muddying the waters, the factory also offers the same item in different quantity packs, including singly, but those at least are a different Amazon SKU on a different Amazon page.
Mitosis creates two identical body cells for growth and repair
Meiosis produces four unique sex cells (gametes) for sexual reproduction.
perpetrate: to commit (a crime or misdeed)
perpetuate: to continue (doing something) or to make perpetual
He perpetrated the error of perpetuating the myth that words don’t matter.
Another science one that confused the heck out me:
Anode: The positive terminal of a battery.
Cathode: The negative terminal of a battery.
And yet…
Anion: A negatively-charged ion.
Cation: A positively-charged ion.
It’s that old opposites-attract thing again: A cation isn’t the negative ion; it’s the ion that’s attracted to negative.
Also confusingly, it’s not pronounced “kayshun.”
That very thing confused me for a long time, too! Because that is, as I learned, incorrect: the anode, resp. cathode, is where (conventional) current enters, respectively leaves, the device. So the positive terminal of a discharging battery is the cathode.
As for cations, the confusing issue is that “conventional” current, as in the above, is defined in terms of positive charges, not electrons. More electrons → negative charge.
The Greek etymologies of the terms can be useful here: the “anode” is the “ana-hodos”, the “way upward or toward”, and the “cathode” is the “kata-hodos”, the “way downward or away”.
So the “anion” is the ion taking that “upward” path to the anode, and the “cation” is on the “downward” path.
Leery - cautious, suspicious
Wary - cautious, susicious
Weary - very tired, worn out
Seen today on the Dope:
Lairy - Br/Aus slang for someone (probably drunk) excitable/aggressive/alarming
Thank you. That’s very useful. Today I learned and it’s still early.
But as with all nouns that are encompassing verb-like directionality, it still is fundamentally ambiguous and there’s no help for that but arbitrary convention.
Why should we interpret e.g. anions as the upward-going thing attracted upwardly towards anodes versus being the upward-going thing being emitted by anodes and traveling upwardly away from anodes?
Why indeed? The answer is because that’s the convention; there is no deeper logic that inevitably favors one interpretation over the other. Etymology & linguistics can provide no answer.
That’s not a criticism of your comment. Just a comment that eventually all coordinate systems have at their foundation an arbitrary privileged direction users simply have to accept and memorize.
In the specific case of all things related to electric charge, we have the historical accident that the directional terminology was standardized before we understood the actual physical charge carrier was what we had, again arbitrarily, long-since labeled as “Negative”. Oops.