Haggard woman facing Queen is thin (5)
I believe the answer is:
sheer
'is thin' is the definition.
(similar in meaning)
'haggard woman facing queen' is the wordplay.
'haggard woman' becomes 'she' (I've seen this in another clue).
'facing' says to put letters next to each other.
'queen' becomes 'ER' (abbreviation for Elizabeth Regina).
'she'+'er'='SHEER'
(Other definitions for sheer that I've seen before include "Absolutely - fine - straight up" , "transparent fabric" , "Nothing other than" , "Deviate (from) - vertical" , "Clear" .)