Meaning of DUAL in English

du ‧ al /ˈdjuː ə l $ ˈduːəl/ BrE AmE adjective [only before noun]

[ Date: 1600-1700 ; Language: Latin ; Origin: dualis , from duo 'two' ]

having two of something or two parts ⇨ single

dual role/purpose/function

The bridge has a dual role, carrying both road and rail.

a dual system of education

dual citizenship/nationality

She has dual nationality, of Canada and Britain (=she is a citizen of Canada and Britain) .

—duality /djuˈæləti, djuˈælɪti $ du-/ noun [uncountable]

Longman Dictionary of Contemporary English.      Longman - Словарь современного английского языка.