I recently came across a text where the electric dipole moment was represented as "d" instead of the more commonly used "p". The reason behind using "d" here is probably that "dipole moment" begins with a "d". However, it also made me wonder why the most commonly used symbol of electric dipole moment is "p" and not "d". What is the reason behind using "p" to represent electric dipole moment?
Also, is there any historical reason for this?