Many men upset Mary (4)

I believe the answer is:

army

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

'many' is the definition.
(thesaurus)

'men upset mary' is the wordplay.
'mary' anagrams to 'ARMY'.
Though, I'm not sure how the anagram is indicated.

Can you help me to learn more?

(Other definitions for army that I've seen before include "Vast number" , "Large host" , "See 7" , "Military land force" , "Ground forces" .)

I've seen this clue in the Evening Standard.

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