- Nephrotoxicity
- Neptunium
- Nernst effect
- Nernst equation
- Nerve
- Nervous system
- Net force
- Net zero emissions
- Neuroendocrine tumors
- Neuroimaging
- Neurons
- Neuroprotection
- Neurosurgery
- Neurotoxicity
- Neurotoxins
- Neurotransmission
- Neurotransmitter
- Neutral axis
- Neutralization
- Neutrino oscillation
- Neutron activation
- Neutron activation analysis
- Neutron capture
- Neutron cross section
- Neutron economy
- Neutron emission
- Neutron flux
- Neutron moderator
- Neutron poison
- Neutron radiation
- Neutron scattering
- Neutron temperature
- Neutron transport
- New Madrid Seismic Zone
- Newton-metre
- Newtonian fluids
- Nickel
- Nickel fluoride
- Nickel sulfide
- Nickel-cadmium battery
- Nickel-metal hydride battery
- Nickeline
- Nicol prisms
- Night
- Night vision
- Nile Red
- Niobium
- Niobium-tin
- Niter
- Nitrate
- Nitrate radical
- Nitratine
- Nitric acid
- Nitric oxide
- Nitriding
- Nitrification
- Nitrifying bacteria
- Nitrile
- Nitrile rubber
- Nitrite
- Nitro compounds
- Nitrogen cycle
- Nitrogen dioxide
- Nitrogen fixation
- Nitrogen narcosis
- Nitrogen oxides
- Nitrogen trifluoride
- Nitrogen-13
- Nitrogenase
- Nitroglycerin
- Nitronic
- Nitronium ion
- Nitrosamines
- Nitrosonium
- Nitrous acid
- Nitrous oxide
- No-slip condition
- Noble gases
- Noble metals
- Nodules
- Noise barrier
- Noise floor
- Noise temperature
- Noise-induced hearing loss
- Nomex
- Non-Newtonian fluids
- Non-ferrous metal
- Non-ionizing radiation
- Non-renewable resources
- Nondestructive testing
- Nonlinear optics
- Nonlinear systems
- Nonmetals
- Nonpoint source pollution
- Nonsteroidal anti-inflammatory drugs
- Normal force
- North American Plate
- Notch
- Nozzle
- Nuclear binding energy
- Nuclear chain reaction
- Nuclear cross section
- Nuclear decommissioning
- Nuclear engineering
- Nuclear envelope
- Nuclear fission
- Nuclear fission products
- Nuclear fuel
- Nuclear fuel cycle
- Nuclear fusion
- Nuclear graphite
- Nuclear medicine
- Nuclear physics
- Nuclear power
- Nuclear power in space
- Nuclear power plants
- Nuclear propulsion
- Nuclear reactions
- Nuclear reactor coolant
- Nuclear reactor core
- Nuclear reprocessing
- Nuclear transmutation
- Nucleation
- Nucleic acid
- Nucleophiles
- Nucleophilic substitution
- Nucleosynthesis
- Nucleotides
- Numerical control
- Nut
- Nutrients
- Nylon
- Nylon 66
- Nystagmus
- O-rings
- OCR
- OEM
- OFDM
- OSB
- OSL
- Obligate anaerobe
- Obsidian
- Occupancy
- Occupational safety and health
- Ocean
- Ocean acidification
- Ocean currents
- Ocean gyre
- Oceanic crust
- Oceanography