Mysterious clue I would follow for old geometrician (6)
I believe the answer is:
euclid
'old geometrician' is the definition.
'Euclid' can be an answer for 'geometrician' (Euclid is an example). I am not sure about the 'old' bit.
'mysterious clue i would follow' is the wordplay.
'mysterious' indicates an anagram.
'i would' becomes 'I'd'.
'follow' is a charade indicator (letters next to each other).
'clue' is an anagram of 'eucl'.
'eucl'+'id'='EUCLID'
'for' acts as a link.
Can you help me to learn more?
(Other definitions for euclid that I've seen before include "Greek father of geometry" , "Geometrician of the 3rd century BC" , "mathematician appears" , "Ancient Greek master of geometry" , "Great Greek mathematician, notable for geometry" .)