Uncomplicated; lacking complexity; taken by itself, with nothing added. • Easy; not difficult. • Without ornamentation; plain. • Free from duplicity; guileless, innocent, straightforward. • Undistinguished in social condition; of no special rank. • Trivial; insignificant. • Feeble-minded; foolish. • Structurally uncomplicated. • Consisting of one single substance; uncompounded. • Being non-trivial, and admitting no proper non-trivial quotients. • Being non-trivial, and having no proper non-trivial normal subgroups (equivalently, no proper non-trivial quotient groups). • Being non-trivial, and having no proper non-trivial submodules (equivalently, no proper non-trivial quotient modules). • Being non-zero, and having no proper non-zero two-sided ideals (equivalently, no proper non-trivial quotient rings). For commutative rings, this definition coincides with that of a field. • Containing more than one element, and such that the only congruences on the structure are the diagonal relation (the equivalence relation a≡b⟺a=b) and the universal relation (the equivalence relation such that a≡b for all a,b). Equivalently, containing more than one element and having no proper non-trivial quotient algebras. • Being non-isomorphic to the terminal object, and such that its only quotient objects (up to isomorphism) are the terminal object and itself. • Being non-abelian and having no proper non-zero ideals. (Note that this is non-equivalent to the usual algebra sense; in particular, the abelian Lie algebra of dimension 1 over any given field is non-trivial and has no proper non-zero ideals, but is by convention not considered simple.) • Equal to a finite linear combination of indicator functions on measurable sets. • Not compound, but possibly lobed. • Using steam only once in its cylinders, in contrast to a compound engine, where steam is used more than once in high-pressure and low-pressure cylinders. (of a steam engine) • Consisting of a single individual or zooid; not compound. • Homogenous. • Mere; not other than; being only.