Old letter found in secret hideaway (3)
I believe the answer is:
eth
'old letter' is the definition.
The definition suggests a singular noun which matches the answer.
'in secret hideaway' is the wordplay.
'in' indicates the answer is hidden within the clue.
'ETH' can be found hidden inside 'secret hideaway'.
'found' acts as a link.
Can you help me to learn more?
(Other definitions for eth that I've seen before include "Old English letter" , "Little Ethel" , "girl" , "Old letter; the (anag.)" , "dated letter" .)