| Acronym | Meaning |
| GCMC | Grand Canonical Monte Carlo |
| GCMFE | Glassy Carbon Mercury Film Electrode |
| GCMS | Gas Chromatography Mass Spectrometry |
| GCNF | Germ Cell Nuclear Factor |
| GCO | General Coupling Operator (in Calcns. Of Vector Coupling For Atoms And Ions) |
| GCOS | Global Climate Observing System (WMO |
| GCP | Good Clinical Practice |
| GCR | Galactic Cosmic Rays (spacecraft Orbit) |
| GCRIO | Global Change Research Information Office |
| GCS | Geo-Common Subsystem (subsystem Of AIRS) |
| GCSEL | Grating-coupled Surface-emitting Laser |
| GCSF | Granulocyte Colony-stimulating Factor |
| GCSOA | Gain-clamped Semiconductor Optical Amplifier |
| GCSOLAR | Green Cross Solar V1.1 |
| GCTE | Global Change And Terrestrial Ecosystems |
| GCTM | Global Chemical Transport Model |
| GCW | Groundwater Circulation Well |
| GD-OES | Glow Discharge Optical Emission Spectroscopy |
| GDA | Glow Discharge Atomization (for Atomic Absorption Spectrometry) |
| GDAAS | Glow Discharge Atomic Absorption Spectrometry |
| GDC | Global Drifter Center (of WOCE Data System) |
| GDC | Glow Discharge Cleaning |
| GDE | General Dynamic Equation |
| GDE | Gas Diffusion Electrode |
| GDEPT | Gene-directed Enzyme Prodrug Therapy |
| GDF | Generalized Density-functional (theory) |
| GDF | Growth Differentiation Factor |
| GDI | Gasoline Direct Injection |
| GDIM | Generalized Diatomics-in-molecules (theory) |
| GDL | Glow Discharge Lamp |
| GDLC | Gel-Glass Dispersed Liquid Crystals |
| GDME | Glycol Dimethyl Ether |
| GDMS | Glow Discharge Mass Spectrometry |
| GDNF | Glial-derived Neurotrophic Factor |
| GDO | Generalized Diatomic Orbital |
| GDOES | Glow Discharge Optical Emission Spectrometry |
| GDOS | Glow Discharge Optical Spectroscopy |
| GDP | Glow Discharge Plasma (for Atomic Emission Spectrometry) |
| GDP | Gross Domestic Product |
| GDP | Guanosine 5'-diphosphate |
| GDR | German Democratic Republic |
| GDR | Giant Dipole Resonance |
| GDR | Glucose Disposal Rate |
| GDR | Geophysical Data Record |
| GDS | Glow Discharge Spectrometer |
| GDT | Generalized Dilatation Transformation (method In Study Of Stationarity Principle For At. And Mol. Resonance States) |
| GDWB | Generalized Distorted-wave Born (approxn. Or Theory) |
| GE-EPMA | Grazing-exit Electron Probe Microanalysis |
| GE-PIXE | Grazing-exit Particle-induced X-ray Emission |
| GEA | Gradient-expansion Approxn. (in Exchange-energy Calcns.) |