Cold shower affected army's devotions (4,5)

I believe the answer is:

hail marys

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

'devotions' is the definition.
Although both the answer and definition are plural nouns, I can't understand how they can define each other.

'cold shower affected army's' is the wordplay.
'cold shower' becomes 'hail' (hail is frozen rain).
'affected' is an anagram indicator.
'armys' is an anagram of 'marys'.
'hail'+'marys'='HAIL MARYS'

Can you help me to learn more?

Want a hint initially instead of a full solution? Install my app