Companion has a time for casual conversation (4)
I believe the answer is:
chat
'casual conversation' is the definition.
(I've seen this in another clue)
'companion has a time' is the wordplay.
'companion' becomes 'cha' (Companion of Honour).
'has' means one lot of letters go next to another.
'a time' becomes 't' (abbreviation).
'cha'+'t'='CHAT'
'for' acts as a link.
(Other definitions for chat that I've seen before include "Inconsequential conversation" , "Communication" , "Tom in 22 [ALSACE]" , "Talking" , "tittle-tattle" .)