lithos (Greek #3037)
a stone (literally or figuratively)
KJV usage: (mill-, stumbling-)stone.
Pronounce: lee'-thos
Origin: apparently a primary word
proskomma (Greek #4348)
a stub, i.e. (figuratively) occasion of apostasy
KJV usage: offence, stumbling(-block, (-stone)).
Pronounce: pros'-kom-mah