Shocked almost certainly by jumping spider (9)
I believe the answer is:
surprised
'shocked' is the definition.
(I know that shocked can be written as surprised)
'almost certainly by jumping spider' is the wordplay.
'almost' means to remove the last letter (most of the word but not all of it).
'certainly' becomes 'sure' (synonyms).
'by jumping spider' becomes 'prised' (I can't explain this - if you can you should believe this answer much more).
'sure' with its final letter removed is 'sur'.
'sur'+'prised'='SURPRISED'
Can you help me to learn more?
(Other definitions for surprised that I've seen before include "Shocked" , "left open-mouthed" , "Took unawares" , "Lost for words" , "Startled" .)