There’s no shortage of translation opinions on Sukha/Dukkha, which are the two most crucial terms for Buddhist worldview arguably: This is dukkha; Nibbāna is sukha.
Margaret Cone, one of the leading Pāli experts, explains Dukkha as following:
dukha mfn. and n. [S. duḥkha; BHS also dukha], 1. (mfn. ) (i ) painful; unpleasant; bringing pain or distress; uneasy, uncomfortable; not what one wants; wrong
Bhante @Sujato once got into the rabbit hole of Sukha meaning “good axle” in old Vedic, referrnig to how chariots were drawn:
So that’s pretty dramatic: 16 occurrences, and all but 2 occur in conjunction with ratha i.e. “chariot”. They are descriptions of the fast, powerful Chariots of the Gods.
So the “chariot” derivation must be correct. And, given that the sense of kha as “hole” is well-established, the sense of “axle-hole” is probably right. But the sense is probably at least somewhat loose, something like “smooth-running”.
The two exceptions both use the term sukhādaya, which seems to mean something like “bringing joy”. If this is correct, they show that the more general sense of sukha as “happiness” was already emerging.
Then the Baudhayana gives us a context for confirming that duḥkha is derived from sukha as the opposite. Why does the negative form not appear in the Vedas? Because they were into the whole “positive thinking” thing! The Vedas are, overwhelmingly, hymns in praise of the Gods, so by praising the smooth running of the Gods’ chariots, the hope is it would help their own chariots run better.
So we have the earliest records of Sukha referring to how smoothly chariots were drawn, to the first signs of its metaphorical usage in Rgv. Bhante argues further:
Never forget, this is normal in language: a term starts with a specific metaphorical basis, but over time the metaphor wears away and becomes thinner, and eventually is lost altogether.
“The Wheel” is the most common symbol of Dhamma, and let’s not forget how Dhammapada opens up:
Intention shapes experiences;
Manopubbaṅgamā dhammā,
intention is first, they’re made by intention.
manoseṭṭhā manomayā;
If with corrupt intent
Manasā ce paduṭṭhena,
you speak or act,
bhāsati vā karoti vā;
suffering follows you,
Tato naṁ dukkhamanveti,
like a wheel, the ox’s foot.
cakkaṁva vahato padaṁ.Intention shapes experiences;
Manopubbaṅgamā dhammā,
intention is first, they’re made by intention.
manoseṭṭhā manomayā;
If with pure intent
Manasā ce pasannena,
you speak or act,
bhāsati vā karoti vā;
happiness follows you
Tato naṁ sukhamanveti,
like a shadow that never leaves.
chāyāva anapāyinī.
After all these breadcrumbs, let me delve deeper into the slang memetic component of Sukha/Dukkha:
Let’s take a look at some of the more popular pairings in contemporary english: Dope/Wack, Cool/Lame, Hot/Cold, Based/Cringe.
The meaning of Dope (originally, “thick sauce”), eventually becoming a drug slang, and even losing that bit. I hardly think anyone saying “That’s dope” means “It’s cocaine”.
Or consider lame for example: Something about disability becoming a slang for bad.
Saying “That’s cold” can mean “That’s cruel”, and saying “That’s cool” might mean “That’s interesting”.
This is not an inquiry about how words can change meanings, but rather how we’re inclined in language to re-create memetic polarities that often have vague “Good/Bad” meanings.
So, treating Sukha/Dukkha as ancient forms of such memetic polarity implying slang words, we might come to terms with how a single word can be used in a wide array of context.
Now as for the particular meaning and taste of Sukha/Dukkha, what follows is my personal impression from dabbling in the suttas:
In line with the chariot origin, the immediate words I feel are relevant is Smooth/Rough. But that’s not the end of it.
There’s also the implication on motion, so it’s not just the smoothness of an object, but a smooth/rough experience itself. Kind of like Good Vibes/Bad Vibes. As Bhante said above, it’s “Smooth/Rough Ride”.
This kind of understanding, I feel, encompasses most of what I’ve seen of Sukha and Dukha being used for.
I’m sorry, but it doesn’t make sense to me how Nibbāna is “pleasure” in the absence of experience. It can be a “Smooth Vibes”, but pleasure it ain’t.
If we try to treat Sukha as a well-defined specific emotion, then Nibbāna can’t be that, I believe. If we understand that Sukha was a memetic word with varying meanings and applications, conveying a general sense of a smooth, seamless experience, rather than a specific emotional state, it makes sense that Nibbāna is the epitome of that.
Same would apply to Dukkha. Dukkha being suffering is often too strong a word for many cases in suttas. In Udana, Buddha is described to experience dukkha because he was surrounded by monastics and students. Saying he was SUFFERING I feel is too strong a vibe (hehe). I think saying “That was rough / a lot of work” is more sensible, I think.
Saying “Everything’s painful” is kind of weird. Saying “Everything brings/is roughness to an otherwise smooth blank state” makes so much more sense to me.
Any kind of ripple on a smooth surface of water is roughness, alien, a barb, a disturbance (i.e. Dukkha).
Sometimes we might mistake certain experiences as “Smooth Rides”, but once we experience even smoother experiences (which is actually just fewer stimuli), then returning to our old “Smooth Experiences”, we realise just how rough and bothersome they are.
After all, how does one increase “Smoothness”? By removing the roughness, of course.
And so, we may understand that absence of any experience is the ultimate smoothness, as any experience is dukkha to that state. “What arises is dukkha, and what ceases is dukkha”.
Now, for a successful religion, it makes sense to make the carrot sexier and the rod deadlier. Smooth/Rough Ride certainly don’t sound as sexy as PLEASURE // SUFFERING.
We also need to have the doctrine as clearly defined, basic as possible, for the largest amount of audiences.
But such considerations might detract from what the spirit of the suttas is trying to convey? And I also think that by having such a strong dichotomy it might make it more difficult to achieve equanimity. Personally, I vibe more with “Life’s a rough ride.” rather than “THIS IS SUFFERING”.
Anyway, these are the thoughts of a dilettante. I’m curious to hear supporting / opposing arguments. 
Metta 
