From Longman Business Dictionary
contractorcon·trac·tor /kənˈtræktəˈkɑːntræktər/ noun [countableC] COMMERCEa person or company that makes an agreement to do work or provide goods in large amounts for another companyThe company has no plans to expand the use of contractors in place of its own staff.
a roofing contractor
→ approved contractor → building contractor → defence contractor → general contractor → haulage contractor → prime contractor