Properly healthy spa (4)
I believe the answer is:
well
I believe this is a triple definition!
'properly' is the first definition.
(thesaurus)
'healthy' is the second definition.
(similar in meaning)
'spa' is the third definition.
(thesaurus)
(Other definitions for well that I've seen before include "Flow up" , "run" , "Source; in good health" , "How one might like one's steak?" , "Very much; plentiful source or supply" .)