First threshold question: is
clonky in the Chihuahua word list? Answer: no.
Second question: is
clonk in the word list? Answer: yes. In fact
clonk,
clonked and
clonking are all in there as common words.
I accept your point that
clonky is listed in some Oxford dictionaries. Although the online Oxford lists it in the
British and World dictionary without a definition - just the direction to "see clonk". However it provides five quite long example sentences that look like they came from real publications. Presumably this is do-it-yourself lexicography. From these examples, I infer that
clonky can have much the same range of meanings as
clunky. It can mean making a knocking sound, but it can also mean cumbersome, awkward, inelegant, etc.
So I think
clonky should be added to our list, but definitely as a rare word. In the massive News on the Web corpus there are only two examples, both referring to cars, like your made-up example, MK. One was from the
British Daily Express website, from earlier this month, where Rowan Atkinson was quoted as using the word about the vintage Citroen cars used in the
Maigret TV series, in which he plays the title role.
Now, as far as I can see, no dictionary lists
clonkier or
clonkiest. This is not necessarily a fatal objection, since the derivation from
clonky is a standard application of English rules, and the meaning of
clonky allows of comparison. But still, these words are very, very rare. There are no examples in the NOW Corpus I mentioned above. In another corpus, Global Web-Based English, I found one instance of
clonkiest, in a reader comment posted on the
KiwiMormon Blog ("Mormon reflections from the antipodes"). "...and a pair of mens shoes, no socks and they were loose and they made the clonkiest noise."
I feel some words are just too rare to accept, and that includes
clonkier and
clonkiest.
While I'm at it, I think I should change
clonk,
clonked and
clonking to rare. These words are not used often, and mainly in Britain, so I don't think they qualify as common words in our sense.