Expensive letter-opener (4)

I believe the answer is:

dear

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'expensive' is the definition.
(similar in meaning)

'letter-opener' is the wordplay.
'letter' becomes 'd'.
'opener' becomes 'ear' (I can't explain this - if you can you should give a lot more credence to this answer).
'd'+'ear'='DEAR'

Can you help me to learn more?

(Other definitions for dear that I've seen before include "Needing plenty of bread" , "Pricey" , "polite form of address" , "Beloved - expensive" , "Costly (but loved!)" .)

I've seen this clue in The Irish Independent.

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