Even the pen holds that many (7)
I believe the answer is:
seventy
'many' is the definition.
Both the definition and answer are adjectives. Perhaps they are linked in a way I don't understand?
'even the pen holds' is the wordplay.
'the pen' becomes 'sty' (both can mean an animal enclosure).
'holds' is an insertion indicator.
'even' put within 'sty' is 'SEVENTY'.
'that' is the link.
Can you help me to learn more?
(Other definitions for seventy that I've seen before include "LXX" , "Threescore and ten" , "Three score years and ten" , "A number" .)