A combining form denoting in the middle, intermediate.
2.
specif. (Chem.), Denoting a type of hydrocarbons which are regarded as methenyl derivatives. Also used adjectively.
3.
(Chem.) Optically inactive due to compensating optical activity at two or more asymmetric centers, often due to a plane of symmetry within the molecular structure; as, meso-tartaric acid.
4.
Attached to a carbon atom located between two hereoatoms in a heterocyclic ring.
... in the air, a stridulating noise is produced by the extreme horny margin of the abdomen being scraped against the rasps. In a great number of long-horned beetles (Longicornia) the organs are situated quite otherwise, the rasp being on the meso-thorax, which is rubbed against the pro-thorax; Landois counted 238 very fine ribs on the ... — The Descent of Man and Selection in Relation to Sex • Charles Darwin
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