It can be ignored ad lib (6)
I believe the answer is:
script
'be ignored ad lib' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'it' is the wordplay.
I cannot really understand how this works, but
'it' could be 't' (abbreviation. e.g. in 'tis) and 't' is found within the answer.
The remaining letters 'scrip' is a valid word which might be clued in a way I don't understand.
This may be the basis of clue (or it may be nonsense).
'can' is the link.
Can you help me to learn more?
(Other definitions for script that I've seen before include "Form of writing" , "Written version of a dramatic composition" , "Piece of handwriting" , "Written text of play or film" , "Words of film etc" .)