araṇi : [f.] a piece of wood for kindling fire by friction.

A.P. Buddhadatta Mahathera, Concise Pali-English and English-Pali Dictionary [available as digital version from Metta Net, Sri Lanka]

araṇi 1
aráṇi f. 'being fitted into' or 'turning round', the piece of wood (taken from the Ficus Religiosa or Premna Spinosa) used for kindling fire by attrition RV. &c. (generally distinction is made between the lower one and the upper one, adharâraṇí and uttarâraṇi, the former may also be meant by araṇi alone without adhara)
• (figuratively) a mother Hariv. (cf. pāṇḍávâraṇi and surâraṇi)
• (is) m. the plant Premna Spinosa L., the sun L., (1), du. f. the two Araṇis (used for kindling the fire) RV. &c
araṇi 2
á-raṇi f. discomfort, pain AV. i, 18, 2

Sanskrit-English Dictionary, by M. Monier William