The English unit of mass is called the Slug.
Yes, I am aware of the Slug as a unit of mass: It has the same dimensions (mass) as the pound (more properly referred to as the "pound-mass" so as to differentiate it from the "pound-force"), so I didn't want to complicate things by introducing it in my (brief, simplified) explanation.
33.2 lb-mass = 1 slug.
All of these units might be more-properly referred to as "Imperial" units - I'm not sure. I have been using SI units and metric units for so long...
Regards,