From ponder + -able.

ponderable

1. (physics) Having a detectable amount of matter; having a measurable mass.
   • 1910, E. T. Whittaker, A History of the Theories of Aether and Electricity, Dublin University Press, published 1910, page 35:

     [T]he imponderability of heat did not appear to the philosophers of the eighteenth century to be a sufficient reason for excluding it from the list of chemical elements; and... there was... doubt... whether caloric was ponderable or not.

2. Worthy of note; significant, interesting.
3. (rare) Heavy; ponderous.
   • 1936, Djuna Barnes, Nightwood, Faber & Faber, published 2007, page 77:

     The very mother's head you swore by in the dock is a heavier head, crowned with ponderable hair.

• (having mass) massive
• (worthy of note) eminent, noteworthy; see also Thesaurus:notable
• (heavy, ponderous) hefty, massive, weighty

• ponder
• ponderous