Guards companies (7)
I believe the answer is:
'guards companies' is the definition.
'escorts' can be an answer for 'guards' (I know this). I'm not certain of the 'companies' bit.
'guards companies' is the wordplay.
'guards' becomes 'escort' (I have seen 'Armed guards' mean 'escort' so perhaps 'guards' could also mean 'escort').
'companies' becomes 's' (I can't explain this - if you can you should give a lot more credence to this answer).
Can you help me to learn more?
(Other definitions for escorts that I've seen before include "Accompanies, perhaps socially" , "Attendants" , "They accompany others" , "Armed guards" , "Accompanies to protect" .)