Learn Polish: Ten młody przedsiębiorca jest współzałożycielem naszego startupu. - This young entrepreneur is the co-founder of our startup.

The prefix współ- translates to "co-" or "jointly". Here it is added to założyciel (founder), which itself comes from the perfective verb założyć (to found or establish). Together they make współzałożyciel (co-founder).

Why is the word for co-founder in the Instrumental case (współzałożycielem) rather than Nominative?

A classic Polish rule that is always good to remember: when you use the verb być (to be) to link a subject to a noun that defines their identity, relationship, or profession, that noun must be in the Instrumental case. Since it is a masculine noun, it takes the -em ending.

Przedsiębiorca ends in "-a" which usually signals a feminine noun. Why do we use the masculine Ten młody here?

Przedsiębiorca (entrepreneur) is a masculine personal noun, much like mężczyzna (man) or kolega (colleague). Because it refers to a male person, adjectives and pronouns describing it must be masculine, even though it follows feminine declension patterns in several grammatical cases.

Why does the English loanword startup take the -u ending to become startupu?