Great skill or knowledge in a particular field or hobby.
‘The scientist has expertise in the field of nuclear fusion.’;
(intransitive) To act as an expert.
Advice, or opinion, of an expert.
(transitive) To give an expert opinion on; to assess.
skillfulness by virtue of possessing special knowledge
give an expert opinion on something
‘a certificate from an expertizing committee’;
expert skill or knowledge in a particular field