Old man's weapons - they are needed for access (9)
I believe the answer is:
passwords
'they are needed for access' is the definition.
The definition suggests an adverb but the answer is not.
'old man's weapons' is the wordplay.
'old man's' becomes 'pa's' (both can mean father).
'weapons' becomes 'swords' (sword is a kind of weapon).
'pas'+'swords'='PASSWORDS'
Can you help me to learn more?
(Other definitions for passwords that I've seen before include "Secret words for authentication" , "Secret letters" .)