Fraction of number that's small, as may be expected (6)
I believe the answer is:
snatch
'fraction' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'number that's small as may be expected' is the wordplay.
'number' becomes 'n' (n can represent any number).
'that's small' becomes 's' (abbreviation - e.g. clothes size).
'as may be' is an anagram indicator.
'expected' becomes 'atch' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'n'+'s'='ns'
'ns' with letters rearranged gives 'sn'.
'sn'+'atch'='SNATCH'
'of' acts as a link.
Can you help me to learn more?
(Other definitions for snatch that I've seen before include "Grasp hurriedly" , "American kidnapping" , "Grab or kidnap" , "Seize abruptly" , "weightlifting move" .)