Hollow

1. (of something solid) Having an empty space or cavity inside.
2. (of a sound) Distant, eerie; echoing, reverberating, as if in a hollow space; dull, muffled; often low-pitched.
3. (figuratively) Without substance; having no real or significant worth; meaningless.
4. (figuratively) Insincere, devoid of validity; specious.
5. Concave; gaunt; sunken.
6. (gymnastics) Pertaining to hollow body position