The vainglorious have not lain with the hearty (8)
I believe the answer is:
vigorous
'the hearty' is the definition.
(thesaurus)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for vigorous that I've seen before include "Powerful, energetic" , "Strong and energetic" , "energetic,strenuous" , "Energetic, strenuous" , "Strong, healthy" .)