Thin imbibing first of miracle cure (6)
I believe the answer is:
remedy
'cure' is the definition.
(synonyms)
'thin imbibing first of miracle' is the wordplay.
'thin' becomes 'reedy' (similar in meaning).
'imbibing' indicates putting letters inside.
'first of miracle' becomes 'm' (rst letter of 'miracle').
'reedy' placed around 'm' is 'REMEDY'.
(Other definitions for remedy that I've seen before include "Medication" , "Something that cures, disease or problem" , "Curative medicine" , "Medicine or therapy to cure" , "Treatment; redress" .)