I must be in position for what comes from the sea (6)
I believe the answer is:
plaice
'what comes from the sea' is the definition.
I can't tell whether this defines the answer.
'i must be in position' is the wordplay.
'i must be' becomes 'i' (I've seen this in other clues).
'in' means one lot of letters goes inside another.
'position' becomes 'place' (synonyms).
'i' going inside 'place' is 'PLAICE'.
'for' acts as a link.
Can you help me to learn more?
(Other definitions for plaice that I've seen before include "A succulent flat-fish" , "N. Atlantic flatfish" , "Edible flatfish" , "Flat fare" , "Flatfish, valued as food" .)