Warmth from the sun as I'm swimming (10)
I believe the answer is:
enthusiasm
'warmth' is the definition.
(thesaurus)
'the sun as i'm swimming' is the wordplay.
'swimming' indicates an anagram.
'the'+'sun'+'as'+'im'='thesunasim'
'thesunasim' with letters rearranged gives 'ENTHUSIASM'.
'from' is the link.
(Other definitions for enthusiasm that I've seen before include "Avidity" , "spirit?" , "Intense and lively interest" , "Zeal" , "Gusto; fervour" .)