Comfortable spring (4)
I believe the answer is:
well
I believe this clue is a double definition.
'comfortable' is the first definition.
(thesaurus)
'spring' is the second definition.
(I've seen this before)
(Other definitions for well that I've seen before include "Issue forth" , "Very much; plentiful source or supply" , "Blooming" , "Abundant source" , "Healthy - water supply" .)