Visuddhimagga XXII-37

822. Assaddhiyakosajjapamādavikkhepasammohānaṃ abhibhavanato abhibhavanasaṅkhātena adhipatiyaṭṭhena indriyaṃ. Assaddhiyādīhi ca anabhibhavanīyato akampiyaṭṭhena balaṃ. Tadubhayampi saddhādivasena pañcavidhaṃ hoti, tasmā pañcindriyāni pañca balānīti vuccanti.

（五根、五力）因为克服了不信、懈怠、放逸、散乱、愚痴，故以称克服的增上之义为「根」。因为不给不信等所胜，故以不动之义为「力」。此两者都依信等而有五种，故说「五根、五力」。

Ñ(XXII,37): 'Faculty' is in the sense of predominance, in other words, of overcoming, because [these states, as faculties] respectively overcome faithlessness, idleness, negligence, distraction, and confusion. 'Power' is in the sense of unwaveringness because [these states, as powers] are incapable of being overcome respectively by faithlessness, and so on. Both are fivefold as consisting in faith, [energy, mindfulness, concentration, and understanding]. That is why 'five faculties' and 'five powers' is said.