Imminent and taking shape, involving most of the firm (11)
I believe the answer is:
forthcoming
'imminent' is the definition.
(synonyms)
'taking shape involving most of the firm' is the wordplay.
'taking shape' becomes 'forming' ('form' can be a synonym of 'take shape').
'involving' is an insertion indicator.
'most of' means to remove the last letter.
'firm' becomes 'co' (a firm is a company).
'the' with its final letter taken off is 'th'.
'th'+'co'='thco'
'forming' enclosing 'thco' is 'FORTHCOMING'.
'and' acts as a link.
(Other definitions for forthcoming that I've seen before include "Communicative" , "Approaching" .)