Woman holding a large rock (5)
I believe the answer is:
shale
'rock' is the definition.
(I know that shale is a type of sedimentary rock)
'woman holding a large' is the wordplay.
'woman' becomes 'shae' ().
'holding' means one lot of letters goes inside another.
'a large' becomes 'L' (eg in clothes sizes).
'shae' enclosing 'l' is 'SHALE'.
(Other definitions for shale that I've seen before include "Soft sedimentary rock" , "Easily-split sedimentary rock" , "Fine pieces of stone on leash" , "Oil-rich rock" , "Layered sedimentary rock" .)