Water traps in front of so-called saint (7)

I believe the answer is:

aquinas

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

'called saint' is the definition.
'aquinas' can be an answer for 'saint' (I've seen this before). I am not sure about the 'called' bit.

'water traps in front of so' is the wordplay.
'water' becomes 'aqua' (I've seen this before).
'traps' indicates putting letters inside.
'front of' suggests taking the first letters (the letter at the front of the word).
The first letter of 'so' is 's'.
'aqua' enclosing 'in' is 'aquina'.
'aquina'+'s'='AQUINAS'

Can you help me to learn more?

(Other definitions for aquinas that I've seen before include "Saintly theologian" , "St. Thomas --, theologian" , "'dumb ox'" , "Saint Thomas --, Italian theologian" , "Sainted theologian" .)

I've seen this clue in The Daily Express.

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