Eels try wriggling briefly (7)
I believe the answer is:
tersely
'briefly' is the definition.
(thesaurus)
'eels try wriggling' is the wordplay.
'wriggling' is an anagram indicator (letters wriggle or move about).
'eels'+'try'='eelstry'
'eelstry' anagrammed gives 'TERSELY'.
(Other definitions for tersely that I've seen before include "using few words" , "In a short and concise manner" , "Abruptly" , "In an abrupt manner" , "In a short or curt manner" .)