- oasis
- nummulite
- oases
- oligocene
- oolite
- oolitic
- orogenesis
- orogenetic
- orogeny
- outlier
- outbreak
- outcrop
- overthrust
- ozocerite
- overfold
- ozokerit
- palaeozoic
- pan
- peneplain
- petroliferous
- Permian period
- picket
- plateau
- plateau level
- plication
- plicate
- pliocence
- pleistocene
- plicated
- plug
- plutonian
- plutonic
- plutonism
- pluvial
- pneumatolysis
- podzol
- point
- post-glacial
- potamology
- polynia
- primary
- primitive
- promontory
- puna
- pyrogenous
- pyrosphere
- quaquaversal
- quaternary
- range rod
- reef
- refuse
- reference mark
- relief
- richter scale
- rod
- rod graduation
- rubble
- rybbly
- saccharoid
- salt diapir
- salt dome
- salt pillow
- salt tectonics
- saliferous
- sand trap
- saturated hydrocarbon
- sandstone
- saprolite
- savanna
- savannah
- secondary
- sediment basin
- sedimentation
- sedimentation rate
- sediment
- sedimentary
- series
- setting out
- shale dome
- shale diapir
- sheet
- shelves
- shift
- sight
- sima
- shelf
- shot point
- sinkhole
- silurian
- sinter
- solifluction
- source rock
- staking
- stalagmite
- start point
- stadiometer
- stage
- stalactite
- strata
- straticulate