OS - a bone; (can also mean) a stone, nut or kernel [Declensions
(not alternative spellings but these determine their position in a
sentence.]: OS, ossem, ossis, ossi, osse, osses, ossum,
ossibus]
osseus - bone-like, made of bone [Adjective, so it has three
genders and their own corresponding declensions: ossei, osseum,
osseis, osseorum, etc.]
tibia - shin bone; (also means a musical instrument, e.g.) pipe
or flute
talus - ankle; ankle bone; knucklebone of a sheep
spina - spine, back; fish-bone
pecten - pubic bone
Remember, each of these words have their own declensions.
Wheelock's Latin Grammar is a good source for beginners.