1. (numeral) one, single, 1 - as in counting out things, in which case each number is preceded by ka.
Ka tīmata te tatau, "Ka tahi, ka rua, ka toru, ka whā, ka rima, ka ono, ka whitu, ka waru, ka iwa." (NM 1928:359). / She began counting them, "One, two, three, four, five, six, seven, eight, nine."
See also tuatahi
2. (numeral) firstly, first of all - when preceded by ka.
Tono rawa ia kia whakaaetia te wahine kia pōti ka tahi; ka rua, i tono hoki ia kia tū hoki he mema wāhine ki roto i te Pāremata Māori (TTR 1994:54). / She requested not only that women be given the vote, but that they be eligible to sit as women members in the Māori parliament.
3. (numeral) first, 1st - when used with this meaning it is preceded by te and followed by o.
E rua anō ngā rā nui o te tau o te Ringatū i hiwaia e ia, arā, ko te huamata i te tahi o Hune me te pure i te tahi o Noema (TTR 1998:27). / There were two special days in the Ringatū year on which he focused, namely, the planting rites (huamata) on the first day of June, and the harvest rite (pure) on the first day of November.
4. one ... the other, each - when repeated.
Kitea te nui o te aurei, o te kuru pounamu ki runga ki te pakihiwi o Tapuae, te here o ngā kākahu o te māhiti, me te wahine a Tapuae, he wahine rangatira hoki, he kākahu kiwi te kākahu, me ngā kōtore huia te rākai ki tahi taha, ki tahi taha, o te māhuna, ko te tiki ki te poho, ko ngā tautau tongarerewa ki tahi pakihiwi, ki tahi (TP 9/1908:3). / An abundance of ivory pins and greenstone ornaments could be seen on Tapuae's shoulder, fastening his garments and his māhiti. His wife too, a well-born woman, was wearing a kiwi cloak, with tail feathers of the huia adorning both sides of her head, a tiki on her breast, and quite a cluster of greenstone drops on each shoulder.
5. (modifier) together, simultaneously, as one, in unison, at the same time, concurrently, both, all - indicates that two or more things are happening or being affected by something at the same time.
Ki te kai te wahine hapū i te hikareti, ka kai tahi te pēpe e noho ake rā i roto i a ia (TP 1/1908:4). / If a pregnant woman smokes cigarettes, the baby that is inside her partakes too.
6. (modifier) actually, no less, absolutely - used after a word to intensify or to add emphasis.
Erangi, kātahi au ka whāki tahi i aua kupu tahi, “Kāore anō he iwi e toitū nei mō tēnei ao.” (JPS 1990:155). / But, then I actually revealed those very words, “There is not yet an undefeated tribe in this world.”
Kei te kaikā rawa ngā taitamariki ki te whakawātea i ngā tēpu. Kāore tahi anō i mutu taku kai, ka kawea taku pereti (HJ 2015:110). / The young people are too eager to clear the tables. I had not even finished my meal when my plate was taken away.