special advisor; special adviser
A formal title for an advisor with a special appointment, often in government, corporate, or organizational settings.
He advises the management as a special advisor to the company.
The government appointed a special advisor on economic policy.
顧問 is a general advisor or consultant, while 特別顧問 is a special advisor with a distinct, often high-level or limited-scope role.
Compound of 特別 (special) and 顧問 (advisor).