1At Sāvatthī. "Bhikkhus, based upon the Himalayas, the king of mountains, the nāgas nurture their bodies and acquire strength. [n.51] As at SN45:151. When they have nurtured their bodies and acquired strength, they then enter the pools. From the pools they enter the lakes, then the streams, then the rivers, and finally they enter the ocean. There they achieve greatness and expansiveness of body. So too, bhikkhus, based upon virtue, established upon virtue, a bhikkhu develops and cultivates the seven factors of enlightenment, and thereby he achieves greatness and expansiveness in (wholesome) states. [n.52] Bojjhaṅga is a compound of bodhi + aṅga. Spk offers a twofold definition: "Enlightenment factors are factors of enlightenment or (factors) of the one being enlightened (bodhiyā bodhissa vā aṅgā ti bojjhaṅgā). What is meant? It is through the assemblage of states consisting in mindfulness … equanimity, arisen at the moment of the mundane and supramundane paths (lokiyalokuttaramaggakkhaṇe) … that the noble disciple is enlightened; therefore (that assemblage of states) is called enlightenment. ‘He is enlightened’ means that he rises up from the sleep of the continuum of defilements; what is meant is that he penetrates the Four Noble Truths or realizes Nibbāna. The enlightenment factors are the factors of the enlightenment consisting in that assemblage of states. Also, the noble disciple who becomes enlightened through the aforesaid assemblage of states is called ‘one being enlightened’ (bodhi). The factors of the one being enlightened are enlightenment factors."
In the Abhidhamma Piṭaka, the Bojjhanga-vibhaṅga (Vibh 227–29) first explains the enlightenment factors by the sutta method in three ways modelled on SN46:3, SN46:46–52 (ii), and the bare vivekanissita formula, respectively. Then it analyses them according to the Abhidhamma method, which treats them solely as factors of the supramundane path (Vibh 229–32). For this reason the definitions in the Abhidhamma commentaries (As 217, Vibh-a 310), parallel to the passage cited from Spk above, omit "mundane" (lokiya) in relation to the path.
The Buddha’s own definition of bojjhaṅga, at SN46:5 below, implies they were originally conceived not as factors that constitute enlightenment (the position taken by the commentaries), but as factors that lead to enlightenment. This is further supported by the sequential account of their origination at SN46:3. Hence comparison of the different strata of early Pali literature shows the usage of the term to have undergone some degree of evolution, from the more general and pragmatic to the more specific and technical.

"And how does a bhikkhu, based upon virtue, established upon virtue, develop the seven factors of enlightenment? Here, bhikkhus, a bhikkhu develops the enlightenment factor of mindfulness, which is based upon seclusion, dispassion, and cessation, maturing in release. sn.v.64 He develops the enlightenment factor of discrimination of states … the enlightenment factor of energy … the enlightenment factor of rapture … the enlightenment factor of tranquillity … the enlightenment factor of concentration … the enlightenment factor of equanimity, which is based upon seclusion, dispassion, and cessation, maturing in release. It is in this way, bhikkhus, that a bhikkhu, based upon virtue, established upon virtue, develops the seven factors of enlightenment, and thereby achieves greatness and expansiveness in wholesome states."

1Sāvatthinidānaṁ. "Seyyathāpi, bhikkhave, himavantaṁ pabbatarājānaṁ nissāya nāgā kāyaṁ vaḍḍhenti, balaṁ gāhenti; te tattha kāyaṁ vaḍḍhetvā balaṁ gāhetvā kusobbhe otaranti, kusobbhe otaritvā mahāsobbhe otaranti, mahāsobbhe otaritvā kunnadiyo otaranti, kunnadiyo otaritvā mahānadiyo otaranti, mahānadiyo otaritvā mahāsamuddasāgaraṁ otaranti; te tattha mahantattaṁ vepullattaṁ āpajjanti kāyena; evameva kho, bhikkhave, bhikkhu sīlaṁ nissāya sīle patiṭṭhāya satta bojjhaṅge bhāvento satta bojjhaṅge bahulīkaronto mahantattaṁ vepullattaṁ pāpuṇāti dhammesu.

Kathañca, bhikkhave, bhikkhu sīlaṁ nissāya sīle patiṭṭhāya satta bojjhaṅge bhāvento satta bojjhaṅge bahulīkaronto mahantattaṁ vepullattaṁ pāpuṇāti dhammesūti? Idha, bhikkhave, bhikkhu satisambojjhaṅgaṁ bhāveti vivekanissitaṁ virāganissitaṁ nirodhanissitaṁ vossaggapariṇāmiṁ; dhammavicayasambojjhaṅgaṁ bhāveti … pe … vīriyasambojjhaṅgaṁ bhāveti … pe … pītisambojjhaṅgaṁ bhāveti … pe … passaddhisambojjhaṅgaṁ bhāveti … pe … samādhisambojjhaṅgaṁ bhāveti … pe … upekkhāsambojjhaṅgaṁ bhāveti vivekanissitaṁ virāganissitaṁ nirodhanissitaṁ vossaggapariṇāmiṁ. Evaṁ kho, bhikkhave, bhikkhu sīlaṁ nissāya sīle patiṭṭhāya satta bojjhaṅge bhāvento satta bojjhaṅge bahulīkaronto mahantattaṁ vepullattaṁ pāpuṇāti dhammesū"ti.

Paṭhamaṁ.