As i understand it Dukkha can be derived from the Sanskrit kha, one meaning of which is some sort of opening, ie 'the axle-hole of a wheel', and the antithetic prefix Duk. Meaning that if you were given a wheel to try for a fit and having tried putting it on your chariot axle you would see that the wheel's 'kha' is a bad fit. Someone would then ask you if the wheel is sukha and you would reply; no it's dukkha. So here it's close to unfitting, bad, wrong, incompatible, unsuitable, disagreeable and ill-fitting.
Sukha would be the opppsite kind of fit. Well-fitting.
I think the ill or the illness are also good translations for dukkha .
From wikipedia
According to Monier-Williams (1964), the etymology of sukha is "said to be su ['good'] + kha ['aperture'] and to mean originally 'having a good axle-hole'...." Thus, for instance, in the Rig Veda sukha denotes "running swiftly or easily" (applied, e.g., to chariots). Sukha is juxtaposed with duḥkha (Sanskrit; Pali: dukkha; often translated as "suffering"), which was established as the major motivating life principles in early Vedic religion.
In the pali we can see this applied to feelings [vedana] denoting pain as 'dukkha vedana' but it's use is broad.
There is a sutta called Dukkha which illustrates this;
"Monks, there are these three kinds of suffering.[1] What three? Suffering caused by pain,[2] suffering caused by the formations (or conditioned existence),[3] suffering due to change.[4] It is for the full comprehension, clear understanding, ending and abandonment of these three forms of suffering that the Noble Eightfold Path is to be cultivated..."
Translator's Notes (Thanissaro)
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- Dukkhataa, an abstract noun denoting "suffering" in the most general sense.
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- Dukkha-dukkhataa, the actual feeling of physical or mental pain or anguish.
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- Sankhaara-dukkhataa, the suffering produced by all "conditioned phenomena" (i.e., sankhaaras, in the most general sense: see BD [Buddhist Dictionary (2nd ed.), by Ven. Nyaa.natiloka, Ven. Nyaa.naponika (ed.), Colombo 1972] s.v. sankhaara I, 4). This includes also experiences associated with hedonically neutral feeling. The suffering inherent in the formations has its roots in the imperfectability of all conditioned existence, and in the fact that there cannot be any final satisfaction within the incessant turning of the Wheel of Life. The neutral feeling associated with this type of suffering is especially the indifference of those who do not understand the fact of suffering and are not moved by it.
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- Viparinaama-dukkhataa, the suffering associated with pleasant bodily and mental feelings: "because they are the cause for the arising of pain when they change" (VM XIV, 35).
I think that in regards to #3 It's noteworthy that it's said; 'sabbe sankhara dukkha' [all formations are dukkha] in the texts. So i think the translator made a slip there writing 'suffering produced by sankhara' and that it should be suffering associated with or suffering denoting all formations [sankhara-dukkha].
All formations are inconstant and to that extent they are flawed in as far as happiness goes, what is flawed that is classed categorically as dukkha.