Army officer's spoken with heart (6)
I believe the answer is:
kernel
'heart' is the definition.
(synonyms)
'army officer's spoken' is the wordplay.
'army officer' becomes 'colonel' (I've seen this before).
'spoken' indicates a 'sounds like' (homophone) clue.
'colonel' is a homophone of 'KERNEL'.
'with' is the link.
(Other definitions for kernel that I've seen before include "Nut's centre" , "Inner part of a seed, the heart of the matter" , "Central or most important part" , "essentials" , "The edible centre of a nut" .)