Fantasist rearmed for exchanges (7)

I believe the answer is:

dreamer

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

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

'rearmed for exchanges' is the wordplay.
'rearmed' anagrams to 'DREAMER'.
However, I'm not clear how the anagram is indicated.

Can you help me to learn more?

(Other definitions for dreamer that I've seen before include "description of an Oxford spire?" , "Fantasist" , "Gerontius" , "Mitty type" , "One who tends to live in an unreal world" .)

I've seen this clue in The Times.

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