Telescope upset mostly Bohemian young woman (8)
I believe the answer is:
spyglass
'telescope' is the definition.
(spyglass is a kind of telescope)
'upset mostly bohemian young woman' is the wordplay.
'upset' says the letters should be written in reverse.
'mostly' means to remove the last letter.
'bohemian' becomes 'gypsy' (Bohemian can mean a Romani person).
'young woman' becomes 'lass' (informal term for a young woman).
'gypsy' with its last letter taken away is 'gyps'.
'gyps' reversed gives 'spyg'.
'spyg'+'lass'='SPYGLASS'
(Other definitions for spyglass that I've seen before include "that magnifies" , "Aid to pirate, perhaps" , "See-through article" , "lookout's aid" , "he can see through it!" .)