Genitive case of an indefinite pronoun pos (some) otherwise obsolete (compare posos); as adverb of place, somewhere, i.e. Nearly -- about, a certain place.
KJV: And being not weak in faith, he considered not his own body now dead, when he was about an hundred years old, neither yet the deadness of Sara's womb:
NASB: Without becoming weak in faith he contemplated his own body, now as good as dead since he was about a hundred years old, and the deadness of Sarah's womb;