1. In biologic classification, the division just below the class (or subclass) and above the family. 2. In a reaction, o. is the sum of the exponents of all the concentration terms in that reaction's rate expression. For example, for the natural decomposition of nitrogen pentoxide, the rate expression is v = −d[N2O5]/dt = k1[N2O5]. Thus, this is a first-o. reaction. A reaction involving two different compounds is often a second-o. reaction (but not necessarily so). Pseudo–first-o. reactions are multiorder reactions in which one of the reactants is in substoichiometric amounts. Cf.:molecularity. 3. The sequence of residues in a heteropolymer. [L. ordo, regular arrangement]
- pecking o. in some species of birds and primates, the establishment of a graded dominance in members of a group by the use of aggression.
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or·der 'ȯrd-ər vt, or·dered; or·der·ing 'ȯrd-(ə-)riŋ to give a prescription for: PRESCRIBE <the doctor \ordered bed rest>
order n a category of taxonomic classification ranking above the family and below the class
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or·der (orґdər) [L. ordo a line, row, or series] a taxonomic category subordinate to a class and superior to a family; see taxon.Medical dictionary. 2011.