ف ل حf-l-ḥ
(ف) فَلَحَ يَفْلَحُ فَلْحًاfalaḥa yaflaḥu falḥan: to cleave, to split; to cleave the earth with a plough (hence فَلَّاحfallāḥ, a farmer). Intransitively, فَلَاحًاfalāḥan: to succeed. (This verb is not used in the Quran.)
Form IV (ifʿāl) اَفْلَحَ يُفْلِحُ اِفْلَاحًاaflaḥa yufliḥu iflāḥan: to succeed, to attain one's goal; generally «فَلَاحfalāḥ» is used as its verbal noun (maṣdar). The original sense is present in that the successful one is he who cleaves through obstacles to reach his goal. ﴿قَدْ اَفْلَحَ الْمُؤْمِنُوْنَ﴾ (Al-Muʾminūn 23:1)
مُفْلِحٌmufliḥ pl. مُفْلِحُوْنَmufliḥūna (active participle, ism fāʿil): successful, one who prospers. ﴿وَاُولٰٓئِكَ هُمُ الْمُفْلِحُوْنَ﴾ (Al-Baqarah 2:5)