What do the commentaries say? Well, we briefly discussed Asl., but U Narada, in his Introduction to “Conditional Relations”, [also weighs in]:
“‘Skilful’. …it cannot apply to moral states, not even to the sensuous, leave alone the lofty and supramundane. The Commentary states that ‘skilful’ is not a suitable meaning….The meaning of ‘kusala’ is also given in the Commentaries on the Suttas…”
He then goes on to list where the word is defined in some 14 places in sutta commentaries, and none of them include “skilful”, and some explicitly say it doesn’t work. Why do you think the commentaries, Ven. Nyanatiloka, and U Narada would so clearly reject ‘skillful’?
And the earlier post in which Asl. and Nyanatiloka were quoted:
In his “Buddhist Dictionary,” Nyanatiloka defines “kusala” as:
“‘karmically wholesome’ or ‘profitable’, salutary, morally good, (skilful). Connotations of the term, according to Com. (Asl), are: of good health, blameless, productive of favourable karma-result, skilful. It should be noted that Com. excludes the meaning ‘skilful’ when the term is applied to states of consciousness.”
[b]Atthasalini indeed explicitly excludes the sense of ‘skilful’ when applied to dhammas:
“…in the phrase ‘moral states’ (kusala dhamma), either ‘wholesome,’ or ‘faultless,’ or ‘productive of happy results’ is a suitable meaning.”
The sense of “skilful” is reserved for contexts such as “You are kusala at the different parts of a chariot,” and “Graceful women who have been trained and are kusala in singing and dancing.”
Why on earth would Asl. make such a careful distinction and not apply ‘skilful’ to mental states? One obvious possibility is that ‘skilful’ could just as easily be applied to the abilities of accomplished murderers, butchers, misers, theives, mechanics, cooks, etc., which have nothing to do with the sense of ‘kusala’ of kusalacittani. Thus, the use of ‘skilful’ in reference to states of consciousness tends to blur the critical moral distinction between kusala and akusala. When applied to mental states, kusala is not “something well done” as opposed to the akusala “something poorly done,” but this is precisely the sense given by skilful/unskilful. I’m going to stick with wholesome/unwholesome or faultless/faulty to help keep the moral distinction clear. After all, proper discernment of kusala vs. akusala is pivotal in the development of samma ditthi.