Definitions
from The American Heritage® Dictionary of the English Language, 4th Edition
 The symbol for the element phosphorus.
 abbr. Genetics parental generation
 abbr. Physics parity
 abbr. pass
 abbr. pawn (chess)
 abbr. Bible Peter
 abbr. petite
 abbr. Physics pressure
from Wiktionary, Creative Commons Attribution/ShareAlike License
 n. The sixteenth letter of the basic modern Latin alphabet.
 n. symbol for phosphorus
 n. symbol for peta
 n. IUPAC 1letter abbreviation for proline
 n. probability
 n. The sixteenth letter of the English alphabet, called pee and written in the Latin script.
 n. The ordinal number sixteenth, derived from this letter of the English alphabet, called pee and written in the Latin script.
 n. park
 n. phone
 n. pager
 n. passenger
 n. Pawn.
 n. A "pure" form of an illegal drug, especially heroin.
 n. methamphetamine
 proper n. The set of all problems that are solvable in polynomial time by a deterministic Turing machine
Etymologies
Examples

Strictly speaking, If P then Q, ~P, therefore ~Q is invalid  modus ponens is only valid if you affirm P; it's not if you deny it.

P(seems TrueTrue)*P(True)+P(seems TrueLie)*P(Lie)
Detect Lie, Bryan Caplan  EconLog  Library of Economics and Liberty

Typically such sentences are conditional sentences such as ˜if P then Q™, though Boethius also treats ˜P or Q™ as hypothetical, apparently because he thinks that disjunction can be translated in terms of a conditional sentence.

Thus, the claim ˜John's statement that P is true™ can be treated as equivalent to (say) ˜P, as John's statement said™.

P (~P/S) EU (~S), assuming that studying's increase in the probability of passing compensates for the effort of studying.

Necessarily P iff, according to the modal fiction, at all worlds, P*, where P* is the possibleworlds paraphrase of P.

P iff according to PW, P*. where “PW” is the fiction of possible worlds, P is any proposition, and P* is its possibleworlds

Others take it to be crucial for any modal interpretation that it also answer questions of the form: Given that a system possesses property P at time s, what is the probability that it will possess property P² at time

P (pr (A) = x) 0 where ˜P™ is the agent's subjective probability function, and ˜pr (A)™ is the assignment that the agent regards as expert.

In that event, ˜Anything is P if and only if it is P²™ comes out true with respect to the actual world but not necessarily true.
Jubjub commented on the word P
Girl
January 2, 2010