- Noun. (obsolete) Mental conception; reflection, consideration. (defdate, 16th-18th c.) .
- Noun. (science) A coherent statement or set of ideas that explains observed facts or phenomena, or which sets out the laws and principles of something known or observed; a hypothesis confirmed by observation, experiment etc. (defdate, from 17th c.) .
- Noun. (uncountable) The underlying principles or methods of a given technical skill, art etc., as opposed to its practice. (defdate, from 17th c.) .
- Noun. (mathematics) A field of study attempting to exhaustively describe a particular class of constructs. (defdate, from 18th c.) .
- Noun. A hypothesis or conjecture. (defdate, from 18th c.) .
- Noun. (countable) (logic) A set of axioms together with all statements derivable from them. ''Equivalently,'' a formal language plus a set of axioms (from which can then be derived theorems).