The dhātu (dhatu; verb-root) ‘arc’ means ‘to pray, to praise and worship’. In one mantra of Ṛgveda (Rigveda), the term has been used in the sense of ‘one who is worthy of worship’. In the hymn dedicated to Indra, composed by Sage Madhucchandā (Madhucchanda), the first line is as follows —
gāyanti tvā gāyatrino arcantyarkaṃ arkinaḥ.
It says, “O Indra! Singers sing to thee, worshipers worship thee, since thou art worthy of such worship’. Here, after using ‘arcanti‘ (archanti) in the verbal form, ‘arka’ has been used as a term deriving from that verb. Further, to denote those who worship, the use of the term ‘arkin’ (in plural arkinaḥ) has reinforced the sense of ‘one who is worshiped’. Yāska,the Vedic lexicon-expert, while determining the nirukti of the term Arka, has said that Arka denotes a god, because a god is to be worshiped. Arka can also mean the hymn or mantra, because the god is worshiped with the help of the hymn. Arka can also denote food or anna, because with food all creatures can be served. And Arka may further mean a tree, which is especially characterised by its bitterness — arko devo bhavati. yadanenārcati. arkamannaṃ bhavati. arko mantro bhavati. yadanenārcati. arcanti bhūtāni. arko vṛkṣo havati. saṃvṛntonkaṭukimnā.

The tree/plant denoted by ‘Arka’ is possibly the plant called Akanda in colloquial Bengali. Since it has been termed ‘vṛkṣa’ (vrikhsa; big tree) in Atharva-veda (6.72.1), scholars have given its scientific name as Colotropis gigantica.