A half buried seed head (3)
I believe the answer is:
bur
'seed head' is the definition.
'bur' can be an answer for 'seed' (I have seen 'Prickly seed ' mean 'bur' so perhaps 'seed' could also mean 'bur'). I am unsure of the 'head' bit.
'a half buried' is the wordplay.
'a half' suggests halving the letters.
'buried' with half the letters taken is 'BUR'.
Can you help me to learn more?
(Other definitions for bur that I've seen before include "sticker" , "Seed-case" , "Prickly seed case" , "small drill" , "Clinging seed case" .)