A special characteristic or quality; prestige, especially via association.
A sealed envelope containing an item whose price is being negotiated.
A commemorative stamped design or inscription on an envelope, other than a cancellation or pre-printed postage.
A capsule containing a pharmaceutical preparation.
A hidden location from which one can observe birds while remaining unseen.
To mark (an envelope) with a commemorative stamped design or inscription.
A perfect standard of beauty, intellect etc., or a standard of excellence to aim at.
A subsemigroup with the property that if any semigroup element outside of it is added to any one of its members, the result must lie outside of it.
A subring closed under multiplication by its containing ring.
A non-empty lower set (of a partially ordered set) which is closed under binary suprema (a.k.a. joins).
A collection of sets, considered small or negligible, such that every subset of each member and the union of any two members are also members of the collection.
A Lie subalgebra (subspace that is closed under the Lie bracket) 𝖍 of a given Lie algebra 𝖌 such that the Lie bracket [𝖌,𝖍] is a subset of 𝖍.
Not actually present, but considered as present when limits at infinity are included.
Optimal; being the best possibility.
Existing only in the mind; conceptual, imaginary.
Pertaining to ideas, or to a given idea.
Perfect, flawless, having no defects.
Teaching or relating to the doctrine of idealism.