A P-argument is the °patient °argument of a physical-effect °verb ('kill', 'break').
This is often simply called "P" (or "P argument" without a hyphen). Note that here it refers to an argument type (a syntactic function, like "direct object"), not to a semantic role (as in Croft 2022; and also in Bickel's work; see Haspelmath 2011).
P role (a.k.a. O role) (SEM) = the patient or patient-like central participant role in the prototypical bivalent event (that is, a breaking event). Example: in Jack broke the window, the window plays the P role in the breaking event. (Section 6.3.1)