Stone entrance? (5)
I believe the answer is:
agate
'stone' is the definition.
(agate is a type of stone)
'entrance?' is the wordplay.
I cannot really see how this works, but
'entrance?' could be 'gate' (type of entrance) and 'gate' is present in the answer.
A single letter 'a' remains which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for agate that I've seen before include "Quartz with bands of colour, used in jewellery" , "Type of quartz" , "rock with bands" , "Quartz variety" , "Semi-transparent stone" .)