I see your peruse, and raise you:
cleave - which means to either 1) separate, or 2) adhere.
Manual of Puissant Skill at Arms
cuirass +1
Enervation spell
You guys need to play more Dungeons and Dragons.
Shibboleth
I had no idea - I always thought it meant something like a monolith and I misused it for years.
mm
Unfortunate, that. The two senses of the word are derived from separate words in Old English which in turn are borrowed from different (but similar-sounding) words from two different germanic dialects.
If you want to force it to make sense, you can always think of a “cleft,” which can be thought of as a joining or a separation, depending on which direction you approach it from. 
For years I thought that the word livid meant someone had a dark red face - liverish coloured, or something. Actually it means the opposite:
All these kings used to die of a “surfeit of lampreys” in the Middle Ages. Doesn’t happen anymore.
I thought it meant fishy, but then what do I know.
I always thought that epitome meant the quintessential instance of something. However my OED says it’s a summary or a representation in miniature.
But, my mistake is apparently so common that recent dictionaries have revised their definitions to agree with what I thought it was anyway.
Dearth sometimes confuses me. It means a shortage; I occasionally think it means the opposite.
Vegetous confuses some folk. (but not me, because I’m a freaky word geek) It means lively or healthy. (It’s synonymous with vegete)
Cool, I found a synonymn for fecund, thanks to you. I use fecund too often in conversation, people think I’m a weirdo or something.
I second “enervated”; also, “pulchritude”.
It was originally a), but through exactly the sort of misunderstanding we’re discussing in this thread, has come to be used to mean b).
So in modern writing it will almost always mean b), but if reading anything written before the 20th century, you would need to consider that it may mean a).
Aye.
yeah, i alway get it confused with:
in·ner·vate Pronunciation (-nûrvt, nr-)
tr.v. in·ner·vat·ed, in·ner·vat·ing, in·ner·vates
- To supply (an organ or a body part) with nerves.
- To stimulate (a nerve, muscle, or body part) to action.
I knew the first couple but the rest seem to have eluded me.
nice
adj. nic·er, nic·est
- Pleasing and agreeable in nature: had a nice time.
- Having a pleasant or attractive appearance: a nice dress; a nice face.
- Exhibiting courtesy and politeness: a nice gesture.
- Of good character and reputation; respectable.
- Overdelicate or fastidious; fussy.
- Showing or requiring great precision or sensitive discernment; subtle: a nice distinction; a nice sense of style.
- Done with delicacy and skill: a nice bit of craft.
- Used as an intensive with and: nice and warm.
- Obsolete.
- Wanton; profligate: “For when mine hours/Were nice and lucky, men did ransom lives/Of me for jests” (Shakespeare).
- Affectedly modest; coy: “Ere… /The nice Morn on th’ Indian steep,/From her cabin’d loop-hole peep” (John Milton).
Callipygiate. I read it in a sentence about someone moving across a room, so I thought it meant a really cool way to move across the room. However, the context, now that I read over it again, supports the real definition, which basically is “to ass one’s way from point A to point B”.
Context sentence: “The phone rang and Miss Irish Ass of 1919 [the novel is set in the 1930s] callipygiated across the room and answered it.” From William Kennedy’s novel Billy Phelan’s Greatest Game.
“Bemused.” The related word “amused” suggests it should mean something similar, or a modification of “amused.”
Instead it means “deep in thought, esp. when perplexed.” I’d never have expected that. I only figured it out a few months ago.
Not British, but otherwise, yes.
Not into SCA, medieval history, royalty worship, or anything similar, either.
Anybody need a lamprey? I got one in my head that really doesn’t belong there. 
Callipygian is one of my favorite adjectives for describing the female form. Well, that and** spathic**. 
Sanguine
Bloodthirsty Optimists of the World Unite!
It’s often difficult to figure which meaning is intended from context.
[Dr. Nick]
Inflammable means flammable? What a country!
[/Dr. Nick]
As others have mentioned, some words (including their dictionary definitions) have changed their meanings over a long period of time.
Originally, nubile meant eligible for marriage. Now it used to describe the overall appearance of a young, shapely, lovely lass.
A visionary originally was someone with unrealisitc, impractical ideas.
Now it seems to be associated with genius whereby Newton, Einstein, etc are categorized as visionaries
i had it all wrong with the phrase lese majeste. I never bothered to look it up but rather tried to translate from context. I thought it meant rendering service to the king. Instead, it means that you’ve done something treasonous. Boy, was I surprised.