ر ک عr-k-ʿ
(ف) رَكَعَ يَرْكَعُ رُكُوْعًاrakaʿa yarkaʿu rukūʿan: to bow, to be bent; the basic sense is any bending done out of reverence or humility, which is why in Arabic poetry it is also said of an old man's stooping. ﴿وَاِذَا قِيْلَ لَهُمُ ارْكَعُوْا لَا يَرْكَعُوْنَ﴾ (Al-Mursalāt 77:48)
رَاكِعٌrākiʿ pl. رَاكِعُوْنَ وَرُكَّعٌrākiʿūna wa-rukkaʿ (active participle, ism fāʿil): one who bows, one who performs rukūʿ. ﴿وَارْكَعُوْا مَعَ الرّٰكِعِيْنَ﴾ (Al-Baqarah 2:43); ﴿تَرٰىهُمْ رُكَّعًا سُجَّدًا﴾ (Al-Fatḥ 48:29) Note: the verb form (bāb) is determined from the Quranic form «يَرْكَعُوْنَyarkaʿūna». This root occurs 13 times in the Quran.