Crossword Genius

Open up head of big fish (6)

Ross

I believe the answer is:

broach

I'm a little stuck... Click here to teach me more about this clue!

'open up' is the definition.
(I've seen this before)

'head of big fish' is the wordplay.
'head of big' becomes 'b' (I can't explain this - if you can you should believe this answer much more).
'fish' becomes 'roach' (roach is a kind of fish).
'b'+'roach'='BROACH'

Can you help me to learn more?

(Other definitions for broach that I've seen before include "Hint" , "Pierce (a cask)" , "crack" , "Start to speak" , "Start to talk about" .)

I've seen this clue in The Sun.
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