Source of antiquated writings stocks a hoard (5)
I believe the answer is:
amass
'hoard' is the definition.
(synonyms)
'source of antiquated writings stocks a' is the wordplay.
'source of' says to take the initial letters.
'writings' becomes 'mss' (more than one MS ie manuscript).
'stocks' indicates putting letters inside (stocks can mean carries or contains).
The initial letter of 'antiquated' is 'a'.
'mss' going around 'a' is 'mass'.
'a'+'mass'='AMASS'
(Other definitions for amass that I've seen before include "Get together" , "Accumulate over time" , "Gather in great quantity" , "Put together" , "Collect or gather" .)