The 'p' could have a different meaning for a variety of languages. 'Puissance' in French, 'Potenz' in German, 'potential' or 'power' in English, 'pondus' or 'potentia' in Latin, or 'Potens' in Danish (probably the Danish one originally, since it was a Danish chemist who first introduced the measurement).
It's very fun that because of the vagueness, various languages can have its meaning directly translated to their own.
The p is for potential, as in potential Hydrogen. pH can be used to establish a concentration of protium (H+) in solution. When learning about pH in school, we used pOH (potential hydroxide) as well to speak about bases.