The term 'BOOT BOTTOM' refers to the bottom of a boot. The two crossword solutions for this term are SOLE (4 letters) and TREAD (5 letters). The SOLE of a boot is the bottom part of the boot that comes into contact with the ground. It is usually made of leather, rubber, or plastic and provides traction and protection from the elements. The TREAD of a boot is the patterned surface on the SOLE that provides grip and traction on different surfaces.