Science (7)
'science' is the definition.
(physics is a kind of science)
This is all the clue.
(Other definitions for physics that I've seen before include "School science subject" , "Science of matter and energy" , "drugs" , "Purges" , "Properties-of-matter science" .)
(Other definitions for chemistry that I've seen before include "Why lovers love" , "A science (of personal attraction?)" , "scientific discipline" , "The science of matter" , "School subject - how individuals react to each other" .)