Greek character, a little bit like some helium (5,8)
I believe the answer is:
alpha particle
'some helium' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.
'greek character a little bit' is the wordplay.
'greek character' becomes 'alpha' (letter from the Greek alphabet).
'a little bit' becomes 'particle' (I've seen this in another clue).
'alpha'+'particle'='ALPHA PARTICLE'
'like' acts as a link.
Can you help me to learn more?
(Another definition for alpha particle that I've seen is " Helium nucleus emitted by radioactivity".)