Commerciante vs. mercante
While 'commerciante' and 'mercante' both refer to individuals involved in trade, they have subtle differences in usage and connotation in modern Italian.
Commerciante
'Commerciante' refers to a shopkeeper or retail merchant, typically involved in small to medium-scale trade of goods or services.
Il commerciante del quartiere ha aperto un nuovo negozio di alimentari.
(The neighborhood shopkeeper has opened a new grocery store.)
Mio zio è un commerciante di mobili antichi.
(My uncle is a dealer in antique furniture.)
Mercante
'Mercante' traditionally refers to a merchant involved in large-scale or international trade, often with historical connotations.
I mercanti veneziani erano famosi per il commercio di spezie dall'Oriente.
(Venetian merchants were famous for trading spices from the Orient.)
Il ricco mercante finanziò la spedizione verso il Nuovo Mondo.
(The wealthy merchant financed the expedition to the New World.)
Summary
While 'commerciante' is commonly used for modern-day retailers and small business owners, 'mercante' often carries a more historical or grand-scale connotation. 'Commerciante' is more frequently used in everyday contexts, whereas 'mercante' might be encountered in historical or literary contexts, or when referring to large-scale international trade.