Prop supine, yet lock behind fine (6,8)
I believe the answer is:
flying buttress
'prop' is the definition.
(I have seen 'Big prop' mean 'flying buttress' so perhaps 'prop' could also mean 'flying buttress')
'supine yet lock behind fine' is the wordplay.
'supine' becomes 'lying' (I am not sure about this - if you are sure you should believe this answer much more).
'yet' becomes 'but' (synonyms).
'lock' becomes 'tress' (both can mean a piece of hair).
'behind' says to put letters next to each other.
'fine' becomes 'f' (abbreviation).
'lying'+'but'+'tress'='lyingbuttress'
'lyingbuttress' put after 'f' is 'FLYING BUTTRESS'.
Can you help me to learn more?
(Other definitions for flying buttress that I've seen before include "Arch" , "part of church?" , "Architectural feature" , "Big prop" , "support?" .)