Blunder by scientist ultimately creating panic (6)
I believe the answer is:
terror
'panic' is the definition.
(I know that panic can be written as terror)
'blunder by scientist ultimately' is the wordplay.
'blunder' becomes 'error' (I've seen this before).
'by' means one lot of letters go next to another.
'ultimately' says to take the final letters.
The final letter of 'scientist' is 't'.
'error' put after 't' is 'TERROR'.
'creating' is the link.
(Other definitions for terror that I've seen before include "Young rascal -- horror" , "Extreme fright or dread" , "Out-of-control child" , "Paralysing fear" , "Overwhelming feeling of fear" .)