Envisaged either part of iron tool (7)
I believe the answer is:
foresaw
'envisaged' is the definition.
(foreseeing is a kind of envisaging)
'either part of iron tool' is the wordplay.
'either' becomes 'or' (I've seen this in another clue).
'part of' indicates putting letters inside (part of the inside).
'iron' becomes 'Fe' (Fe is the chemical symbol for iron).
'tool' becomes 'saw' (saw is a kind of tool).
'or' put into 'fe' is 'fore'.
'fore'+'saw'='FORESAW'
(Other definitions for foresaw that I've seen before include "Anticipated" , "Predicted" , "Expected" .)