Definition of dual adjective from the Oxford Advanced American Dictionary

 

dual

 adjective
adjective
NAmE//ˈduəl//
 
[only before noun]
 
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having two parts or aspects his dual role as composer and conductor She has dual nationality (= is a citizen of two different countries). The piece of furniture serves a dual purpose as a cabinet and as a table. see also dual-purpose Which Word?double / dualThese adjectives are frequently used with the following nouns:
double ~dual ~
bedpurpose
doorsfunction
figuresrole
standardsapproach
thicknesscitizenship
Dual describes something that has two parts, uses, or aspects. Double can be used with a similar meaning, but when it is used to describe something that has two parts, the two parts are usually the same or very similar. Double, but not dual, can describe something that is made for two people or things, or is twice as big as usual.
See the Oxford Advanced Learner's Dictionary entry: dual