Couch potato originally to share nuts (6)
I believe the answer is:
phrase
'couch' is the definition.
(I know that couch is a more specific form of the action phrase)
'potato originally to share nuts' is the wordplay.
'originally' says to take the initial letters.
'to' says to put letters next to each other.
'nuts' indicates an anagram (nuts can mean crazy).
The first letter of 'potato' is 'p'.
'share' anagrammed gives 'hrase'.
'p'+'hrase'='PHRASE'
(Other definitions for phrase that I've seen before include "Group of words as unit" , "Present" , "Sentence unit" , "Short musical passage" , "Express in words" .)