Reading perhaps lies within safety mark on metal dipstick (6)
I believe the answer is:
cretin
'dipstick' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.
'reading perhaps lies within safety mark on metal' is the wordplay.
I cannot quite see how this works, but
'reading' could be 'r' (one of the traditional three R's of education) and 'r' is located in the answer.
'within' could be 'in' and 'in' is located in the answer.
'metal' could be 'ce' (Ce is an example) and 'ce' is present in the leftover letters.
A single letter 't' 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 cretin that I've seen before include "Idiot!" , "fool" , "soft" , "Halfwit" , "Charlie" .)