In the original text, this is not a “wu-” form, but it is frequently used in parallel to “wuwei”; I have chosen to render it with an English phrase analogous to “action without force”.

This treatment may have distorted its meaning somewhat more than that of “wuwei”. “Teaching without words” is at least more plausibly literal than “no-action”; my best guess is at a primary intent was teaching by indirection (as in “by avoiding the one, he chooses the other”), and possibly teaching things that can’t be readily explained. Note that, as the original text is poetry, it is more likely than not to have more than one intended meaning.

At any rate, the meaning I have chosen to emphasize is that of communicating without ego. Whether or not this was a connotation of the original text, this meaning does seem to fit readily into many of the places where the phrase occurs. Also, it is a genuine problem that is hard to solve if you don’t have the knack, and one where a Daoist attitude seems likely to be effective.