What priests offered queen wearing undies (6)
I believe the answer is:
shrift
'what priests offered' is the definition.
(archaic term for confession)
'queen wearing undies' is the wordplay.
'queen' becomes 'r' (r is abbreviation regina. e.g. in ER ).
'wearing' is an insertion indicator.
'undies' becomes 'shift' (historically, an undergarment).
'r' inserted inside 'shift' is 'SHRIFT'.
(Other definitions for shrift that I've seen before include "confession, this might be short" , "form of confession" , "Given a short one, one is dismissed" , "Pardon?" , "Absolution and penance (now usually short!)" .)