They serve to provide many helpful devices (5)
I believe the answer is:
maids
'they serve to' is the definition.
The definition suggests an adverb but the answer is not.
'many helpful devices' is the wordplay.
'many' becomes 'M' (Roman numeral for a thousand).
'helpful devices' becomes 'aids' (I am not sure about this - if you are sure you should believe this answer much more).
'm'+'aids'='MAIDS'
'provide' acts as a link.
Can you help me to learn more?
(Other definitions for maids that I've seen before include "Lasses" , "Female domestic servants" , "Getting women in service" , "girls!" , "Female domestics" .)