/ ˈtɜːʃəri; NAmE ˈtɜːrʃieri; -ʃəri/ adjective
third in order, rank or importance :
the tertiary sector (= the area of industry that deals with services rather than materials or goods)
( BrE )
tertiary education (= at university or college level)
—compare primary , secondary
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WORD ORIGIN
mid 16th cent.: from Latin tertiarius of the third part or rank, from tertius third.