This is the 4514th most frequent Catalan word.
neix
"Neix" means "is born."
In this sentence, "neix" refers to the origin or starting point of the river, metaphorically indicating its "birth" from a source.
El riu neix a les muntanyes.
The river originates in the mountains.
Here, "neix" is used in the literal sense to indicate the act of being born into the world.
Quan un nen neix, tothom està feliç.
When a child is born, everyone is happy.
In this context, "neix" metaphorically describes the emergence or inception of an idea stemming from a motivating factor.