No, you cannot only use the return ticket.
To guarantee that the airline keeps your return ticket, you are required to travel on the first part of your trip and all the way to your final destination.
For example, if you booked London - New York - London, you cannot use the return as a single ticket from New York. You must fly London - New York first to be able to travel back on the ticket from New York to London.
The airline will automatically cancel all return flights and you will not be eligible for a refund if the outbound flight is not used.