いずこ

Etymology
→ →  →

Shift from -derived of the same meaning.

By analogy with locative pronouns and, both of which end in -ko, the final -u of izuku became -o. Furthermore, the final the -ku and -ko of both aforementioned pronouns ultimately share cognancy with Old Japanese, which would have been pronounced as at that time.

Pronoun

 * 1)   where, whence, whither, which
 * ,,  ( 5, twenty-ninth day of the first month)
 * [Note: some manuscripts use of the same meaning instead of izuko.]
 * 1)   anywhere, everywhere, somewhere
 * 1)   anywhere, everywhere, somewhere
 * 1)   anywhere, everywhere, somewhere
 * 1)   anywhere, everywhere, somewhere