A little cogitation is enjoyable (7)
I believe the answer is:
amusing
'enjoyable' is the definition.
Both the answer and definition are adjectives. Perhaps there's an association between them I don't understand?
'a little cogitation' is the wordplay.
'a' becomes 'amp' (A is the symbol for the amp or ampere).
'little' means to remove the last letter (the word is not quite complete).
'cogitation' becomes 'using' (I am not sure about this - if you are sure you should believe this answer much more).
'amp' with its last letter removed is 'am'.
'am'+'using'='AMUSING'
'is' acts as a link.
Can you help me to learn more?
(Other definitions for amusing that I've seen before include "Pleasantly diverting" , "Entertaining, pleasing" , "Giving entertainment" , "might be funny" , "Entertaining in a mild way" .)