... another is turning up with gamma, oddly (5)
I believe the answer is:
sigma
'another is' is the definition.
I can't tell whether this definition defines the answer.
'turning up with gamma oddly' is the wordplay.
'turning' shows that the letters should be reversed in order.
'up' becomes 'is' (I've seen this in other clues).
'with' is a charade indicator (letters next to each other).
'oddly' indicates alternate letters (letters in the odd-numbered positions are used).
The alternating letters of 'gamma' are 'gma'.
'is' backwards is 'si'.
'si'+'gma'='SIGMA'
Can you help me to learn more?
(Other definitions for sigma that I've seen before include "Greek letter used as summation sign" , "Greek character" , "Foreign character" , "Agism of the Greek letter" , "Greek letter used as a symbol for summation" .)