Something that is four times the usual number, amount, size, etc.
A figure-skating jump with four revolutions in the air.
To multiply by four.
To increase by a factor of four.
To provide four parallel running lines on a given stretch of railway.
Being four times as long, as big or as many of something.
A sequence of four elements.
One of a group of four, particularly one of four babies born from the same mother during the same birth.
A tuplet of four notes.
A cycle for carrying four riders, arranged so that all the riders can assist in the propulsion.