approximation
noun [ C, usually singular ]
uk/əˌprɒksɪˈmeɪʃən/ usa figure that is close to a particular number or time but not exactly that number or time:
Sales-tax receipts provide an approximation of retail sales.
something that is similar to another thing but not exactly the same:
approximation to sth A closer approximation to the truth is that he started out as a genuine entrepreneur.