Top in English, fifth in History, German unknown, with pass in Science (7)
I believe the answer is:
ecology
'science' is the definition.
(ecology is a kind of science)
'top in english fifth in history german unknown with pass' is the wordplay.
'top in english fifth in history' becomes 'eo' (I can't justify this - if you can you should believe this answer much more).
'german' becomes 'g' (abbreviation).
'unknown' becomes 'y' (algebra).
'with' is an insertion indicator.
'pass' becomes 'col' (col is a term for a mountain pass).
'eo'+'g'+'y'='eogy'
'eogy' placed around 'col' is 'ECOLOGY'.
'in' acts as a link.
Can you help me to learn more?
(Other definitions for ecology that I've seen before include "Scientific study of living things in their environment" , "Science of the interaction of organisms and their environment" , "The environment as it relates to living organisms" , "Study of creatures etc in relation to environment" , "Branch of biology" .)