Hint to head of espionage — move stealthily (6)
I believe the answer is:
tiptoe
'move stealthily' is the definition.
(I've seen this before)
'hint to head of espionage' is the wordplay.
'hint' becomes 'tip' (synonyms).
'head of' suggests taking the first letters.
The first letter of 'espionage' is 'e'.
'tip'+'to'+'e'='TIPTOE'
(Other definitions for tiptoe that I've seen before include "or get a bit higher on this?" , "Walk delicately - musically through the tulips" , "Walk quietly on the balls of one's feet" , "Move carefully" , "Walk stealthily" .)