IT company starting to invent new revolutionary clouds (5)
I believe the answer is:
nimbi
'clouds' is the definition.
(nimbus is a kind of cloud)
'it company starting to invent new revolutionary' is the wordplay.
'it company' becomes 'ibm' (computer company).
'starting to' indicates taking the first letters.
'revolutionary' says the letters should be written backwards.
The initial letters of 'invent new' is 'in'.
'ibm'+'in'='ibmin'
'ibmin' backwards is 'NIMBI'.
(Other definitions for nimbi that I've seen before include "Rain-bearing clouds" , "Rain clouds - halos" , "Rain-clouds" , "They may surround the head" , "Dark things" .)