a person who is authorised to verify affidavits and other legal documents

A person entitled to administer oaths; solicitors who have a practising certificate and Fellows of the Institute of Legal Executives have the powers of a Commissioner for Oaths

An officer appointed by the Lord Chancellor to administer (i.e. to take) Oaths and Affirmations and Declarations to persons who com to them for this purpose. This office is now redundant since all practising solicitors can now do so without having to be commissioners. Older firms of solicitors may still designate themselves "Solicitors and Commissioners for Oaths"