Regular international among male side gaining runs
I believe the answer is:
mainstream
'regular' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how one could define the other.
'international among male side gaining runs' is the wordplay.
I cannot really understand how this works, but
'international' could be 'i' (abbreviation eg in IMF) and 'i' is found in the answer.
'male' could be 'man' (man is a kind of male) and 'man' is found within the leftover letters.
'side' could be 'r' (abbreviation for right) and 'r' is present in the answer.
The remaining letters 'steam' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for mainstream that I've seen before include "type of jazz" , "Relating to what is normal or standard" , "conventional activities" , "In accordance with what is normal or standard" , "Current" .)