p

from The American Heritage® Dictionary of the English Language, 5th Edition.

• abbreviation piano (musical direction)
• abbreviation proton
• noun The 16th letter of the modern English alphabet.
• noun Any of the speech sounds represented by the letter p.
• noun The 16th in a series.
• noun Something shaped like the letter P.
• noun A hypothesized textual source of certain portions of the Pentateuch that have a formulaic style, contain genealogical lists and descriptions of rituals, and use the name "Elohim" to refer to God.

from The Century Dictionary.

• noun An abbreviation of Pharmacopœia Britannica, British Pharmacopœia.
• noun An abbreviation of the Latin partes æquales, equal parts.
• noun An abbreviation of Privy Councilor; of police constable.
• noun An abbreviation of Pharmacopœia Edinensis, Edinburgh Pharmacopœia; of Protestant Episcopal.
• noun An abbreviation of Pharmacopœia Dublinensis, Dublin Pharmacopœia.
• noun An abbreviation: of post-office;
• noun (nautical) of petty officer.
• noun An abbreviation: of post meridiem, ‘after noon or midday’ (also P. M., p. m.): frequently used as synonymous with afternoon or evening;
• noun of postmaster;
• noun of peculiar meter.
• noun An abbreviation of participial adjective, employed in this dictionary.
• The sixteenth letter and twelfth consonant of the English alphabet, having a corresponding position in other alphabets.
• As a medieval numeral, 400; with a dash over it , 400,000.
• As a symbol: In chem., the symbol for phosphorus.
• In mathematics, the Greek capital II denotes a continued product.
• Thus, , for which Π (1 + m) is also written, denotes the product (1 + m) m (m − 1) … 3.2.1. The small Greek letter π denotes the ratio of the circumference to the diameter, or 3.14159265359 + . This notation was introduced by Euler. The other form of the Greek minuscule, ω%26, denotes in astronomy the longitude of the perihelion.
• An abbreviation: Of post in P. M., post meridiem, afternoon, and P. S., postscript.
• [lowercase] Of page (past participle standing for pages).
• [lowercase] In music, of piano, softly (past participle standing for pianissimo, very softly)
• [lowercase] In a ship's log-book, of passing showers.
• [lowercase] In zoology: Of partim. In dental formulas, same as pm. In ichthyology, of pectoral (fin). In echinoderms, of polyplacid.
• In medicine, of (Optic) papilla; pupil; pugillus, handful.
• noun An abbreviation of postscript; (theatrical) of prompt-side.
• An abbreviation of Post Adjutant.
• noun An abbreviation of the Latin Philosophiæ Baccalaureus, Bachelor of Philosophy;
• noun of Primitive Baptist.
• The initial of pressure, used in formulæ for fluid pressure, as of liquids or gases upon an area. In British and American writings it is usually expressed in pounds per square inch or pounds per square foot, the zero of pressures being the vacuum line as given by the barometer, or about 14.7 pounds below the pressure of the atmosphere. In metric units it is usually expressed in kilograms per square centimeter.
• In mechan., a symbol for power.
• In psychophysics, the symbol for the Fechnerian time-error.
• An abbreviation: Of population.
• Of the Latin pars, apart.
• [lowercase or cap.] Of participle.
• [lowercase or cap.] Of past.
• Of the Latin pater, father.
• [lowercase or cap.] Of penny.
• [lowercase or cap.] Of pint.
• [lowercase or cap.] Of pipe.
• [lowercase or cap.] Of pole.
• Of the Latin pondere, by weight.
• In electro-technics, of power.
• Of president.
• Of prince.