Smart guy keeping IBM unsettled still (7)
I believe the answer is:
alembic
'still' is the definition.
(I've seen this before)
'smart guy keeping ibm unsettled' is the wordplay.
'smart guy' becomes 'alec' (as in the phrase 'smart Alec').
'keeping' indicates putting letters inside (some letters kept inside).
'unsettled' indicates an anagram.
'ibm' anagrammed gives 'mbi'.
'alec' placed around 'mbi' is 'ALEMBIC'.
(Other definitions for alembic that I've seen before include "Old retort" , "Still" , "Old distillation vessel" .)