From shachar; a dawning, i.e. (figuratively) juvenescence -- youth.
see HEBREW shachar
H7839. shacharuth
שַׁחֲרוּת noun feminine according to DEComm. RüetschiKau blackness, namely, of hair (so ᵑ7), i.e. (RV) prime of life (which Wild allows); usually dawn of youth (II. שׁחר); — Ecclesiastes 11:10 (+ יַלְדוּת).