Start to study more sinuous snake (7)
I believe the answer is:
slither
'snake' is the definition.
(thesaurus)
'start to study more sinuous' is the wordplay.
'start to' suggests taking the first letters.
'more sinuous' becomes 'lither'.
The first letter of 'study' is 's'.
's'+'lither'='SLITHER'
(Other definitions for slither that I've seen before include "Slide, slip" , "Move smoothly over a surface with a twisting motion" , "Slide on slippery surface" , "Move like a snake" , "Slide (like a snake)" .)