Calm sort of current in South American river (7)

I believe the answer is:

placate

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

'calm sort' is the definition.
'placate' can be an answer for 'calm' (placating is a kind of calming). I'm not certain of the 'sort' bit.

'current in south american river' is the wordplay.
'current' becomes 'ac' (alternating current).
'in' indicates putting letters inside.
'south american river' becomes 'plate' (I've seen this before).
'ac' going within 'plate' is 'PLACATE'.

'of' is the link.

Can you help me to learn more?

(Other definitions for placate that I've seen before include "Pale cat could pacify" , "Make less angry" , "'Pacify, appease (7)'" , "Make calm, conciliate" , "Mollify, appease" .)

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

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