A hypocycloid in which the radius of the rolling circle is a quarter of the radius of the fixed circle. It has parametric equations x = a cos3t, y = a sin3t, where a is the radius of the fixed circle.
An astroid
- ribbon bomb
- ribbon cable
- ribbon development
- ribbon diagram
- ribbon jasper
- ribbon lakes
- ribbon microphone
- ribbons
- ribbon worm
- riboflavin
- ribonuclease
- ribonucleic acid
- ribonucleoprotein
- ribose
- ribosomal RNA
- ribosome
- riboswitch
- ribotyping
- ribozyme
- ribulose
- ribulose bisphosphate
- Ricardian equivalence
- Ricardo, David (1772–1823)
- Ricci, Matteo (1552–1610)
- Riccioli, Giovanni Battista