A rangatira is a chief, the suffix -tanga implies the quality or attributes of chieftainship, and the addition of intensifier tino in this context means the phrase can be translated as 'absolute/unqualified chieftainship'.
In article one of the Treaty's English text the Maori signatories ceded their sovereignty to the British Crown. The Maori text of the translation used the missionary neologism 'kawanatanga' (= 'governorship') to approximate this concept. This word had been invented by Bible translators, to explain Pontius Pilate's authority in Judaea.
In article two of the Treaty, the Maori text assured the signatories that their tino rangatiratanga would remain undisturbed, along with their continued possession of their lands and other taonga.
This apparent inconsistency in the Maori text of the Treaty has led to much debate as to whether the Maori signatories intended to cede their sovereignty to the British Crown at all, and if in fact some vestigial Maori sovereignty remains.