anamatagga : [adj.] one whose beginning is unknown.

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

Anamatagga (adj.) [ana (= a neg.) + mata (fr. man) + aggā (pl.). So Dhammapāla (avidit -- agga ThA 289); Nāṇakitti in Ṭīkā on DhsA 11; Trenckner, Notes 64; Oldenberg, Vin. Texts ii.114. Childers takes it as an + amata + agga, and Jacobi (Erzähl. 33 and 89) and Pischel (Gram. § 251) as a + namat (fr. nam) + agga. It is Sanskritized at Divy 197 by anavarāgra, doubtless by some mistake. Weber, Ind. Str. iii.150 suggests an + āmrta, which does not suit the context at all]. Ep. of Saṃsāra "whose beginning and end are alike unthinkable", i. e., without beginning or end. Found in two passages of the Canon: S ii.178, 187 sq. = iii.149, 151 = v.226, 441 (quoted Kvu 29, called Anamatagga -- pariyāya at DhA ii.268) and Th 2, 495, 6. Later references are Nd2 664; PvA 166; DhA i.11; ii.13, 32; Sdhp 505. [Cp. anāmata and amatagga, and cp. the English idiom "world without end". The meaning can best be seen, not from the derivation (which is uncertain), but from the examples quoted above from the Saṃyutta. According to the Yoga, on the contrary (see e. g., Woods, Yoga -- system of Patañjali, 119), it is a possible, and indeed a necessary quality of the Yogī, to understand the beginning and end of Saṃsāra].

Pali-English Dictionary, TW Rhys Davids, William Stede,