Crossword Genius

Book sizes up snake wound (6)

Ross

I believe the answer is:

psalms

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

'book sizes' is the definition.
'psalms' can be an answer for 'book' (I've seen this before). I'm not certain of the 'sizes' bit.

'up snake wound' is the wordplay.
'up' is a reversal indicator (in down clue: letters go upwards).
'snake' becomes 'asp' (asp is a kind of snake).
'wound' becomes 'lms' (I can't explain this - if you can you should give a lot more credence to this answer).
'asp' backwards is 'psa'.
'psa'+'lms'='PSALMS'

Can you help me to learn more?

(Other definitions for psalms that I've seen before include "OT book" , "David's hymns" , "Holy songs" , "Biblical songs" , "They're heard in church" .)

I've seen this clue in The Telegraph.
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