when there is no word to describe the thing you wish to describe, you should probably just make one up.

i learned several amazing geography facts today. here is one of them:

the earth isn't perfectly spherical. there's a bit of a bulge because of the centrifugal force of the earth's rotation (imagine pressing a tennis ball on a table, and you'll have a good idea of how it's shaped.) there's nothing on earth that's the shape of...well...the earth. so, some geographers decided to come up with a name for the earth's shape: geoidal. the definition of geoidal? earth-shaped. the earth? yeah. it's geoidal. yep, earth-shaped.

update: edited to enhance scientific accuracy.