ODO: rude {adjective} = 4. {attributive} {chiefly British} Vigorous or hearty
OED: Etymology: < Anglo-Norman rud, Anglo-Norman and Old French, Middle French rude, Old French (Lyons, rare) ruide (French rude) ... (of a person's body) robust, vigorous, strong (1426) ...
I wish to dig deeper than the definition, which I already understand and so ask NOT about. I heed the Etymological Fallacy. What are right ways of interpreting or rationalizing this meaning, in order to intuit or naturalise it, and to help me remember?
Does this definition 4 (of positive connotation) jar with the negative definitions of 'rude' ?
Just as Etymonline and Wordreference.com don't, OED above only states, but doesn't explain, the definition. Above I excerpted OED's lengthy entry; please advise if I should display more.
Footnote: I first encountered this in 'rude health' here, but please beware that I ask about this definition in general, and NOT only this set phrase.