- Packing density
- Paddle wheels
- Pagodas
- Pain
- Paint
- Paint thinner
- Pair distribution function
- Palaeochannel
- Paleosols
- Palladium
- Palladium acetate
- Palladium on carbon
- Palygorskite
- Pancreas
- Paper mills
- Paperboard
- Parabolas
- Parabolic antenna
- Parabolic reflectors
- Paraboloids
- Paracellular transport
- Parachutes
- Paraffin wax
- Parallel axis theorem
- Parallelogram
- Parallelogram law
- Paramagnetism
- Parametric equations
- Parametric surface
- Parapets
- Parathyroid hormone
- Parenchyma
- Paresthesia
- Parietal cells
- Paris' law
- Parisite-
- Parking lot
- Parkinson's disease
- Parquet
- Partial differential equations
- Partial pressure
- Particle board
- Particle physics
- Particle radiation
- Particle size
- Particle-size distribution
- Particulates
- Partition coefficient
- Pascal
- Pascal's law
- Passivation
- Passive cooling
- Passive fire protection
- Passive infrared sensor
- Passive solar building design
- Passive ventilation
- Path integral formulation
- Pathogen
- Pathology
- Patina
- Patio
- Pauli Exclusion Principle
- Pavement
- Pavement engineering
- Pavement management
- Pavers
- Pearlite
- Pearson symbol
- Peat
- Pebble
- Pebble-bed reactors
- Peening
- Pegmatite
- Pellet fuel
- Pelletizing
- Penetrating oil
- Penicillamine
- Pentane
- Pentlandite
- Pepsin
- Peptic ulcer disease
- Peptide bonds
- Peptide synthesis
- Peptides
- Per capita
- Per- and polyfluoroalkyl substances
- Peracetic acid
- Perchlorate
- Percussion caps
- Perfluorohexane
- Perfluorooctanesulfonic acid
- Perfluorooctanoic acid
- Perfluoropolyether
- Performance per watt
- Perfume
- Pericarditis
- Periclase
- Peridotite
- Perimeter
- Periodic table
- Periodic trends
- Periprosthetic
- Peristalsis
- Peristaltic pump
- Perlite
- Permanganate
- Permeability
- Permeable paving
- Permeation
- Permissible stress design
- Permittivity
- Permutation group
- Perovskite
- Perovskite solar cells
- Peroxide
- Peroxydisulfate
- Perpendicular
- Perseverance
- Persistent organic pollutants
- Personal computers
- Personal watercraft
- Perspiration
- Perthite
- Perturbation
- Perturbation theory
- Pervaporation
- Pervious concrete
- Pesticides
- Petalite
- Petri dishes
- Petrochemicals
- Petrographic microscope
- Petrography
- Petroleum coke
- Petroleum ether
- Petroleum naphtha
- Petroleum products
- Petroleum reservoir
- Petrology
- Petrophysics
- Pewter
- Pharmaceutical industry
- Pharmaceutics
- Pharmacology
- Pharmacy
- Pharynx
- Phase diagrams
- Phase modulation
- Phase problem
- Phase rule