Attempt to imprison every queen could be this (9)
I believe the answer is:
treachery
'be this' is the definition.
The definition suggests a singular noun which matches the answer.
'attempt to imprison every queen' is the wordplay.
'attempt' becomes 'try' (synonyms).
'to imprison' means one lot of letters goes inside another.
'every' becomes 'each' (synonyms).
'queen' becomes 'er' (abbreviation for Elizabeth Regina).
'each'+'er'='eacher'
'try' enclosing 'eacher' is 'TREACHERY'.
'could' is the link.
(Other definitions for treachery that I've seen before include "Deceptiveness" , "perfidious conduct" , "lack of loyalty" , "Betrayal of trust" , "Two-timing" .)