This is the 289th most frequent Italian word.
lunedì
Monday.
In this sentence, 'lunedì' is used to refer to a specific day of the week, in this case 'Monday', when the described activity occurs.
Lunedì andiamo al cinema.
On Monday, we are going to the cinema.
In this context, 'lunedì' is part of an expression to indicate a habitual action that happens on Mondays.
Tutti i lunedì, partecipiamo al corso di yoga.
Every Monday, we participate in the yoga class.
Here, 'lunedì' depicts the events or routines associated with Monday mornings, used as a singular masculine noun with a definite article.