Crossword Genius

Person buying drink welcomed by ship's finance officer (9)

Ross

I believe the answer is:

purchaser

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

'person buying' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.

'drink welcomed by ship's finance officer' is the wordplay.
'drink' becomes 'cha' (cha can mean tea).
'welcomed by' means one lot of letters goes inside another (I've seen this in other clues).
'ship's finance officer' becomes 'purser' (I've seen this in another clue).
'cha' going within 'purser' is 'PURCHASER'.

Can you help me to learn more?

(Other definitions for purchaser that I've seen before include "Buyer" , "Punter" , "I'll buy" , "he's bought" , "customer" .)

I've seen this clue in The Telegraph.
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