- recurring
- reffection
- reducible
- reduction
- regression
- remainder
- regular
- repeater
- representation
- representative
- residua
- residual
- residuum
- resolution
- resolve
- result
- resultant
- reversible
- revolution
- rhomboid
- rhomboidal
- rider
- right
- reversibility
- reversion
- rhombus
- rhumb line
- residue
- rhomb
- rhombi
- root
- roulette
- rooting
- scalene
- scalar
- secant
- segment
- sector
- sequent
- series
- sequence
- sequential
- set
- side
- similar
- simplex
- sine
- sinistrorsal
- sinistrorse
- similarity
- sinusoidal
- skew
- slide-rule
- sliding rule
- solution
- solve
- square
- square-matrix
- state
- straight angle
- subtangent
- subtrahend
- submultiple
- subring
- subequilateral
- subharmonic
- subtraction
- strophoid
- supplement
- supplemental
- supplementary
- surd
- surface
- subtend
- subtract
- subtractive
- summation
- tangency
- tangent
- term
- ternary
- tetragon
- tetragonal
- tetrahedral
- tetrahedron
- theorem
- third
- transcendental
- transformation
- translate
- transposable
- transpose
- transposition
- trapeze
- trapezium
- translational
- trapezoid
- trigonal
- trihedral
- trihedron