It's adopted by heartless foe? (6)
I believe the answer is:
enmity
'it's adopted by heartless foe?' is the definition.
I can't tell whether this defines the answer.
'it's adopted by heartless foe?' is the wordplay.
'it's' becomes 'it' (I've seen this in other clues).
'adopted by' indicates putting letters inside (I've seen this in other clues).
'heartless' suggests removing the centre.
'foe?' becomes 'enemy' (enemy is a kind of foe).
'enemy' with its middle removed is 'enmy'.
'it' inserted inside 'enmy' is 'ENMITY'.
Can you help me to learn more?
(Other definitions for enmity that I've seen before include "Hate; aversion" , "Personal hostility" , "Hostility between opposing groups or nations" , "Hostility between opposing people or countries" , "Hostility, ill-will" .)