Treason by earl at resort (8)
I believe the answer is:
betrayal
'treason' is the definition.
(synonyms)
'by earl at resort' is the wordplay.
'resort' indicates anagramming the letters.
'by'+'earl'+'at'='byearlat'
'byearlat' is an anagram of 'BETRAYAL'.
(Other definitions for betrayal that I've seen before include "Breaking of trust" , "Treacherous divulgence" , "Breach of trust" , "Act of disloyalty" , "Treacherous act" .)