Fibrous tissue is revolutionary and different (5)
I believe the answer is:
sinew
'fibrous tissue' is the definition.
(sinew is a kind of fibrous tissue)
'is revolutionary and different' is the wordplay.
'revolutionary' says the letters should be written in reverse (letters revolve around).
'and' means one lot of letters go next to another.
'different' becomes 'new' (similar in meaning).
'is' written backwards gives 'si'.
'si'+'new'='SINEW'
(Other definitions for sinew that I've seen before include "fibre" , "Muscular strength" , "It indicates strength" , "Strength; tendon" , "As synonym for 'strength'" .)