Otherwise, do not remain as part of fraction (11)
I believe the answer is:
denominator
'part of fraction' is the definition.
The answer and definition can be both quantities as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'otherwise do not remain' is the wordplay.
'otherwise' is an anagram indicator.
'do'+'not'+'remain'='donotremain'
'donotremain' with letters rearranged gives 'DENOMINATOR'.
'as' acts as a link.
Can you help me to learn more?
(Other definitions for denominator that I've seen before include "Lower half of fraction (could be common!)" , "Lower number" , "Divisor" , "what's under the line?" .)