An orthographical variation of 'omnam -- in (very) deed; of a surety.
see HEBREW 'omnam
H552. umnam
אֻמְנָם adverb (from אֹמֶן by affix ָ ם) verily, truly, indeed, always in interrogative Genesis 18:13 (J), elsewhere הַאֻמְנָם Numbers 22:37 (E) 1 Kings 8:27; 2 Chronicles 6:18; Psalm 58:2.