ball of the thumb

/B AO1 L AH0 V DH AH0 TH AH0 M/
noun
  1. 1

    (anatomy, informal) The fleshy portion, opposite the nail, of the first segment (first phalange) of the human thumb.

  2. 2

    (anatomy) The most fleshy portion of the palm of the human hand, located adjacent to the second joint of the thumb: the thenar eminence.