Clear about Queen coming, perhaps (12)
I believe the answer is:
peradventure
'perhaps' is the definition.
('peradventure' can be a synonym of 'perhaps')
'clear about queen coming' is the wordplay.
'clear' becomes 'pure' ('pure' can be similar in meaning to 'clear').
'about' means one lot of letters goes inside another.
'queen' becomes 'er' (abbreviation for Elizabeth Regina).
'coming' becomes 'advent' ('advent' can be a synonym of 'coming'**).
'er'+'advent'='eradvent'
'pure' going around 'eradvent' is 'PERADVENTURE'.
(Other definitions for peradventure that I've seen before include "Possibly (archaic)" , "Maybe" , "by chance" , "perhaps" .)