Envisage instruments originally employed in Enigma variation (7)
I believe the answer is:
imagine
'envisage' is the definition.
(synonyms)
'instruments originally employed in enigma variation' is the wordplay.
'originally' indicates taking the first letters.
'employed in' means one lot of letters goes inside another.
'variation' indicates anagramming the letters.
The initial letter of 'instruments' is 'i'.
'enigma' anagrammed gives 'imagne'.
'i' going within 'imagne' is 'IMAGINE'.
(Other definitions for imagine that I've seen before include "Suppose; think up" , "Suppose; conceive" , "See something that doesn't exist" , "A Gemini? (anag)" , "Enigma, I? (anag)" .)