Charming words to put into letters (5)

I believe the answer is:

spell

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

'charming words' is the definition.
'spell' can be an answer for 'words' (I have seen 'Magic words ' mean 'spell' so perhaps 'words' could also mean 'spell'). I'm unsure of the 'charming' bit.

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for spell that I've seen before include "Put letters in right order" , "Magic incantation" , "Magic formula - period of time" , "Short time, splinter" , "... mean" .)

I've seen this clue in The Globe and Mail.

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