I will of course get it checked if it doesn't go but googling suggests a ganglion.
It's on my palm but just before it meets the base of my index finger of my right hand. Smooth, firm, feels like a pea. I can move it from side to side and it doesn't hurt. I'm wondering if it's caused by regularly lifting 4kg hand weights while working out? I had something similar on the top of one of the fingers of the other hand a couple of years ago on the joint nearest the nail and it disappeared after a couple of months.
Thanks.