Stone some used to flag a terrace (5)
I believe the answer is:
agate
'stone' is the definition.
(agate is a type of stone)
'some used to flag a terrace' is the wordplay.
'AGATE' is hidden in amongst the letters.
But, I am not sure how this is indicated.
Can you help me to learn more?
(Other definitions for agate that I've seen before include "Semi-precious quartz" , "Banded ornamental stone" , "Type of quartz" , "Hard stone with concentric bands of colour" , "Quartz with bands of colour, used in jewellery" .)