Please consult a competent qualified attorney. I am not such but have discussed this topic with my law-type-person in the past (we are both Canadian).
There is a Common Law progression in severity from mere negligence to gross negligence to wilful misconduct.
mere negligence == failure to do what a reasonably prudent person would do in similar circumstance OR to do something that a reasonably prudent person would not do in similar circumstance.
gross negligence == a very marked departure from the normal behaviour or standards of a reasonable and competent person in similar circumastance OR circumstance where risk of mishap/consequence is greater than normal therefor requiring greater than ordinary care that was not taken.
willful misconduct == voluntary and intentional misconduct or reckless behaviour.
Important to note: increasingly these and similar terms are being specifically defined within/for each contract. Given the uncertainty of circumstance and differences between professions Contractual Definitions are becoming common. Also some industry organisations specify such terms for use between members.