A seer I heard (3)
I believe the answer is:
eye
'a seer' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.
'i heard' is the wordplay.
'heard' shows a homophone (sound like).
'i' sounds like 'EYE'.
Can you help me to learn more?
(Other definitions for eye that I've seen before include "'Cast a cold ... on life, on death' (Yeats)" , "Ogle" , "Orb" , "1 across, 4 across, for example" , "Location of 11dn" .)