shopping center vs sales outlet

shopping center and sales outlet both are nouns.

Word	Noun	Adjective	Verb	Adverb
shopping center	Yes	No	No	No
sales outlet	Yes	No	No	No

As nouns, sales outlet is a hypernym of shopping center; that is, sales outlet is a word with a broader meaning than shopping center:

shopping center: mercantile establishment consisting of a carefully landscaped complex of shops representing leading merchandisers; usually includes restaurants and a convenient parking area; a modern version of the traditional marketplace
sales outlet: a place of business for retailing goods

Other hypernyms of shopping center include mercantile establishment, outlet, retail store.

shopping center (noun)	sales outlet (noun)
mercantile establishment consisting of a carefully landscaped complex of shops representing leading merchandisers; usually includes restaurants and a convenient parking area; a modern version of the traditional marketplace	a place of business for retailing goods