Foreign character recalled spook with wild lion (7)
I believe the answer is:
ypsilon
'foreign character' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.
'recalled spook with wild lion' is the wordplay.
'recalled' shows that the letters should be reversed in order (to recall can mean to bring something back).
'spook' becomes 'spy' (I've seen this in another clue).
'with' is a charade indicator (letters next to each other).
'wild' indicates an anagram.
'spy' in reverse letter order is 'yps'.
'lion' is an anagram of 'ilon'.
'yps'+'ilon'='YPSILON'
Can you help me to learn more?
(Another definition for ypsilon that I've seen is " 20th Greek letter".)