Etymology of sukha and duHkha

[Ulrich T. Kragh]

The recent discussion thread on chariots inspired me to bring up the
following question, which I have been wondering about:

Do you have any comments on the etymologies of the Sanskrit words sukha
"happiness" and duHkha "misery"?

As far as I know, the standard etymology for sukha is based on the earliest
occurrence of this word, namely in Rgveda; e.g. Monier-Williams (p. 1220,
entry 'sukha') writes:

"Sukha, mfn. (said to be fr. 5.su+3.kha and to mean originally 'having a
good axle-hole;' possibly a PrAkRit form of su-stha, q.v.; cf. duHkha) ..."

The word kha itself seems simply to have the basic meaning of "hole" or
"aperture", also an aperture of the human body; again, MW gives reference to
Rgveda, where kha occurs (unfortunately, I haven't got a concrete reference
for you here) in sense "the hole in the nave of a wheel through which the
axis runs" (MW p. 334, entry "kha").

Thus, I think the standard etymology for sukha "happiness" is taken to be
"having a good axle-hole", i.e. having a functioning (or perhaps fast)
chariot, and thus in the extended meaning thereby meaning "to be happy".
Oppositely, duHkha would refer to the state of not having such a good hole.

However, I get my doubts when seeing this etymology. Having a background in
Tibetan studies, I know that the basic meaning of the word kha (exact same
spelling and pronounciation) in Tibetan and possibly in other Himalayan
languages is again "hole", but usually referring to "the mouth".

I believe that the same meaning can be seen in the Skr. word mukha "mouth,
face", which likewise occurs in Rgveda.

This led me to think that sukha could actually be derived from kha in the
sense of mouth (lit. "good mouth") in the extended meaning of "being
nourished or satisfied with food" and thus being "happy", whereas duHkha
similarly would come to mean "hungry" and thus "unhappy".

Since sukha and duHkha are such fundamental terms in human existence, I find
such an etymology more believable than the perhaps far-fetched "having a
good axle-hole".

I would very much appreciate clarification on these terms.

With best regards,
Ulrich T. Kragh
University of Copenhagen