D. (usually preceded in English by the) -- The abbreviation for the Spanish honorific Don, formerly a mark of high esteem for a distinguished Christian hidalgo or nobleman. In current Spanish, it may be used for mild respect, say, as in shopkeeper to customer; it is still the usual form to refer to a known priest, as in French Dom. The old use is roughly comparable to the style "Honourable" in British custom, although the analogy is a loose one, at best. The female version is DĒ for Doņa.
Don or Doņa is attached to the Christian name, and the person is then addressed as such. For example, if Seņor Diego de la Vega is to be addressed as a don, then the correct form of address would not be *"don de la Vega", but "don Diego".
In Catalan, the equivalent form is en/na.