Up and down

“Are you up for that?” “Yeah, I’m down”

Dust. Dust the shelf, dust the loaf with flour.

Well, this is the opposite thing (same word meaning opposite) but if you ask me it's the same.

EDIT: For some that fit better:

• thaw / unthaw
• terminate / exterminate
• valuable / invaluable
• caregiver / caretaker

Two examples where erroneous usage has resulted in this paradox:

• Regardless and irregardless

• "I couldn't care less" and "I could care less"

"flammable" and "inflammable" both describe an object that can easily catch on fire.

WHAT A COUNTRY!

Literally means either literally or figuratively, and context doesn't really help.

To bone and to debone both mean to remove bones from something, typically food.

This is kinda the opposite to what you are asking: awesome and awful used to mean the same thing IIRC, both being something filling you with awe. Later the meanings split between positive and negative.

Same with terrible and terrific.

suck and blow

Near miss and near hit both mean a close call.

Sanction can mean a punishment or an authorization.

Came up in a DND game where a devil's contract said the players crossing the region would be sanctioned, or something like that. Players thought it meant they had permission, fine print said they would be punished.

One that sorta works:

it's all uphill / downhill from here -> it's only going to get worse

One way mirror and two way mirror

In French there is personne (someone) and personne (no one), plus (more) and plus (no more)

Cleave

Antiautonym is what you're looking for.

For Australians, yeah, yeah nah, yeah yeah nah, nah, nah yeah nah, nah nah yeah, all have subtly different positive and/or negative meanings, often dependent on the situation.

Garnish can either be an enhancing addition such as in a dish, or to take something away such as garnishing wages.

You can lease/rent something to a tenant... Or you can lease/rent something from someone.

The informal definition of "literally" is an exaggeration of something that is not literally true. Inn other words, figuratively.

The undead are dead.

Not the original question you asked, but fits in with your edit:

Priceless and worthless are opposites

Slightly different, but single words meaning multiple conflicting things seem to come to mind more readily:

• Drop meaning both to abandon or release a product
• Table meaning both put something aside or putting up for discussion
• Literally meaning both literal and figurative

inflammable and flammable

Ravel and unravel can both mean to take apart something that was knitted or woven.

I literally can't believe this thread.

• Restless and Restful.

• mark and demarcate. I love this one.

• also, limit and delimit

• a bit of a stretch but i can imagine someone saying "You're a natural" and "you're a freak" to express someone being abnormally talented at something on their first try.

"You're a natural at rock climbing. You're a rock climbing freak. A freak at rock climbing."

They're called "contranyms". Easy to find examples once you know that

https://en.wikipedia.org/wiki/Contronym