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os·ti·um

(ŏstē-əm)

n. pl. os·ti·a (-tē-ə)

1. A small opening or orifice, as in a body organ or passage.

2. Any of the small openings or pores in a sponge, through which water is drawn in.

[Latin ōstium, door, opening, from ōs, mouth; see ōs- in the Appendix of Indo-European roots.]

Indo-European & Semitic Roots Appendices

Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:

Indo-European Roots

Semitic Roots

The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.

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