There is no really adequate definition of singular term. Here are some definitions proposed by different writers:
- A term that tells us which individual is being talked about. (John Stuart Mill, Arthur Prior, P. F. Strawson) 
- A term that is grammatically singular, i.e. a proper name (proprium nomen), a demonstrative pronoun (pronomen demonstrativum) or a demonstrative pronoun with a common name (cum termino communi). (William of Ockham)
- A term that is inherently about the object to which it applies or refers. (Gottlob Frege) 
- A term that is true "in the same sense" of only one object. (Peter of Spain)
Works cited Edit
- Frege, G. (1892) "On Sense and Reference", originally published as " Über Sinn und Bedeutung" in Zeitschrift für Philosophie und philosophische Kritik, vol. 100, pp. 25-50. Transl. Geach & Black 56-78.
- Mill, J.S., A System of Logic, London 1908 (8th edition).
- Petrus Hispanus, Summulae Logicales, ed. I. M. Bochenski (Turin, 1947) – also quoted in Prior 1976
- Prior, A.N. The Doctrine of Propositions & Terms London 1976
- Strawson, P.F. "On Referring", Mind 1950 pp. 320-44.
- William of Ockham, Summa logicae Paris 1448, Bologna 1498, Venice 1508, Oxford 1675