Delicate insect crossing one manuscript (6)
I believe the answer is:
flimsy
'delicate' is the definition.
(thesaurus)
'insect crossing one manuscript' is the wordplay.
'insect' becomes 'fly' (fly is a kind of insect**).
'crossing' indicates putting letters inside.
'one' becomes 'i' (Roman numeral).
'manuscript' becomes 'ms' (abbreviation for manuscript).
'i'+'ms'='ims'
'fly' placed around 'ims' is 'FLIMSY'.
(Other definitions for flimsy that I've seen before include "Fragile; weak" , "Light and thin, easily torn or broken" , "Lacking strength and solidity" , "Not strong" , "Light and thin, material or argument, perhaps" .)