IUPAC definition : A chemical species or molecular entity having an available pair of electrons capable
of forming a covalent bond with a hydron (proton) (see Brønsted base) or with the
vacant orbital of some other species (see Lewis base).;
A chemical species or molecular entity having an available pair of electrons capable
of forming a covalent bond with a hydron (proton) (see Brønsted base) or with the
vacant orbital of some other species (see Lewis base).