Perhaps from rakak; softness, i.e. (figuratively) fear -- faintness.
see HEBREW rakak
H4816. morek
מֹ֫רֶךְ noun [masculine] weakness (Köii. 1, 98); — Leviticus 26:36 I will send ׳מ into (ב) your heart (i.e. make you timid, fearful, compare √ 1a, רַךְ 2).