From sharar in the sense of twisted, i.e. Firm; obstinacy -- imagination, lust.
see HEBREW sharar
H8307. sheriruth
שְׁרִירוּת, usually שְׁרִרות noun feminine firmness, always = stubbornness; only construct ׳שׁ, followed by ׃לֵב : Jeremiah 9:13; 13:10; 23:17; Deuteronomy 29:18; Psalm 81:13 (שְׁרִירוּת); ׳שׁ הָרָע ם לִָ Jeremiah 3:17; 7:24; 11:8 (׳שְׁרִי), so (לִבּוֺ) 16:12; 18:12.