42,772 articles
Methylone
Methylone, also known as bk-MDMA or MDMC, is a synthetic cathinone acting as a psychostimulant and empathogen, and is the beta-keto analog of MDMA, differing only by a ketone group.
Methylparaben
Methylparaben, also known as methyl 4-hydroxybenzoate or Nipagin, is a paraben used as an antimicrobial preservative in cosmetics, foods, and pharmaceuticals; it also occurs naturally in blueberries.
Methylsulfonylmethane
Methylsulfonylmethane (MSM), also called dimethyl sulfone, is a naturally occurring organosulfur compound found in trace amounts in foods and sold as a joint-health dietary supplement.
Methyltrichlorosilane
Methyltrichlorosilane, also called trichloromethylsilane, is a colorless, volatile organosilicon liquid produced as a by-product of silicone manufacture and used as a silicone crosslinker and coating agent.
Methysergide
Methysergide, sold as Sansert and Deseril, is a semisynthetic ergot alkaloid and serotonin antagonist that became the first effective preventive drug for migraine after its 1959 introduction.
Metirosine
Metirosine, known in the United States as metyrosine, is a synthetic amino acid that inhibits tyrosine hydroxylase and is used to reduce catecholamine production in pheochromocytoma.
Metol
Metol, also known as methylaminophenol, is a crystalline chemical used as a developing agent in black-and-white photography since the 1890s, most often paired with hydroquinone in MQ developers.
Metolachlor
Metolachlor is a chloroacetanilide herbicide, EPA-registered since 1976, applied preemergence in corn, soybeans, and cotton; since 1997 most product is the more active S-metolachlor, while the EU withdrew approval in 2024 over groundwater concerns.
Meton of Athens
Meton of Athens, son of Pausanias, was a 5th-century BC Athenian astronomer who introduced the Metonic cycle, 19 tropical years equaling 235 lunar months, at Athens in 432 BC.
Metonic cycle
The Metonic cycle, named for the Athenian astronomer Meton, is a 19-year period containing almost exactly 235 lunar months, the basis of lunisolar calendars and Easter dating.
MetOp-C
MetOp-C is a European weather satellite launched on a Soyuz rocket from Kourou in 2018, the third and final satellite of the first-generation EUMETSAT Polar System.
MetOp-SG
MetOp-SG (Metop Second Generation) is a series of six European polar-orbiting weather satellites serving weather forecasting and climate monitoring into the 2040s, with the first launched in August 2025.
Metre
The metre, also spelled meter (French mètre), is the SI base unit of length, defined since 1983 as the distance light travels in vacuum in 1/299,792,458 of a second.
Metre–tonne–second system of units
The meter–tonne–second system (MTS) is a coherent metric unit system based on the meter, tonne, and second, introduced in France in 1919 and the Soviet Union in 1933.
Metribuzin
Metribuzin, sold under the trade names Sencor and Lexone, is a selective triazinone herbicide that controls grass and broadleaf weeds by inhibiting photosynthesis at photosystem II.
Metric dimension (graph theory)
The metric dimension of a graph, also called the locating number, is the smallest set of vertices whose distances uniquely identify every vertex, introduced in 1975.
Metric Diophantine approximation
Metric Diophantine approximation is the branch of number theory that classifies, by Lebesgue measure, which real numbers admit infinitely many rational approximations of a prescribed quality.
Metric interval temporal logic
Metric interval temporal logic (MITL) is a real-time temporal logic, introduced by Alur, Feder, and Henzinger in 1996, whose temporal operators carry non-singular time intervals, making satisfiability decidable in EXPSPACE.
Metric measure space
A metric measure space, or mm-space, is a mathematical structure pairing a metric space with a measure, written (X, d, μ), letting geometry and analysis interact.
Metric prefix
A metric prefix is a symbol placed before a unit of measurement to multiply it by a power of ten; SI prefixes run from quecto (10−30) to quetta (1030).
Metric space
A metric space, also known as metric geometry, is a set with a distance function satisfying symmetry and the triangle inequality, introduced by Fréchet in 1906 and central to convergence and continuity.
Metric system
The metric system is a decimal system of measurement based on powers of ten, created in France in the 1790s and now maintained worldwide as the SI.
Metric temporal logic
Metric temporal logic (MTL) is a formal specification language that extends linear temporal logic with time bounds, letting requirements such as 'every request must be answered within 5 seconds' be checked mechanically.
Metric tensor
A metric tensor is a smoothly varying inner product on the tangent spaces of a manifold that measures lengths, angles, and distances; it underlies Riemannian geometry.
Metric tensor (general relativity)
In general relativity, the metric tensor, or spacetime metric, is the symmetric tensor field that defines distances, times, and causal structure, determined by the Einstein field equation.
Metric time
Metric time (decimal time) is a system dividing the day into ten hours, one hundred minutes, and one hundred seconds. It was enacted by revolutionary France in 1793.
Metrication in the United Kingdom
Metrication in the United Kingdom is the process of replacing imperial units with the metric system, made official policy in 1965 and still incomplete today.
Metrizable space
A metrizable space (metrisability, metrizability) is a topological space whose topology is generated by some metric, so that it is homeomorphic to a metric space.
Metrologia
Metrologia is an international peer-reviewed journal on the science of measurement, founded in 1965 and published on behalf of the Bureau International des Poids et Mesures by IOP Publishing.
Metrology
Metrology is the science of measurement, covering the definition of internationally accepted units, their realization as physical standards in national laboratories, and the traceability of everyday instruments, including legal metrology for trade devices.