What initiates disquiet about fellow in computing etc for certain (8)
I believe the answer is:
definite
'certain' is the definition.
(similar in meaning)
I cannot understand how the rest of the clue works.
(Other definitions for definite that I've seen before include "Sure, certain" , "Certain or explicit" , "Positive, certain" , "Unmistakable" , "Certain, decisive" .)