Adverb from 'omen; verily -- indeed, no doubt, surely, (it is, of a) true(-ly, -th).
see HEBREW 'omen
H551. omnam
אָמְנָם adverb (= אֻמְנָם) verily, truly, in asseverations 2 Kings 19:17 (= Isaiah 37:18) Job 19:4-5, 34:12; 36:4; Ruth 3:12, also ironical Job 9:2; 12:2.