Examples of o- ovo ‘pig’   okhe ‘tiger’   osi ‘dog’   otu ‘ox’   oho ‘kind of domestic fowl’   oku ‘kind of squirrel with three marks on its back’   oto ‘dewlap’   ocu ‘male genital’   opfo ‘father’   oro ‘basket’   okhro ‘dao’   oto ‘necklace’   omo ‘pumpkin’   oru ‘uncultivated and typically wooded area     outside the village gate’   odo ‘paddy field’       Examples of i -  ihõ ‘snake’   ipre ‘elephant’   ihi ‘goat’   imi ‘tail’   ihõ ‘spear’   icü ‘jackal’
The only morphological function they may be said to have is that they mark ‘relational’ nouns, nouns whose referents can be alienably or inalienably possessed, as is clear in the examples above. ‘Classifiers’ mark semantic classes of lexical items. So o- could be considered some sort of a classifier. It is however not a classifier for two reasons : 1. Classifiers cover the whole language and this does not. Even the semantic class of relational nouns is not marked exhaustively. The following exemplify objects which can be possessed but whose nouns are not marked morphologically [by o- or i-].
koso ‘cat’ cohć ‘buffalo’ fola ‘navel’ pinouo ‘brother’ pisü ‘basket’ piko ‘knife’ cisa ‘bangle’ pito ‘cucumber’
2.	Some other word-classes are also marked by o-, though not exhaustively. So o- is not a nominal marker either.
Postpositions othi ‘behind’ adverbs ovu ‘adv of number’
Grierson [1903 : 3,2 : 452] calls o- an ‘otiose’ segment which means it is superfluous or functionless. Native speakers feel so too, some of them wanting the analyst to delete it when the language is recorded !
However, the initial o- of Mao Naga nouns does have a phonological function.
Its phonological function is to fulfill the requirement of disyllabicity of Mao nouns. Mao Naga nouns are necessarily nonmonosyllabic and typically disyllabic3 . o- occurs [as does i-] only with monosyllabic roots and never with di- or polysyllabic roots. Even monosyllabic loan words which meet the structural requirement of the Mao syllable are converted into disyllables by prefixing o-
ca ą oca ‘tea’
When other morphemes occur with words with o-, o- is automatically dropped and is replaced by these morphemes thus yielding the canonical disyllabic structure. See 3.3.1.1 for contexts which trigger such deletion. Nouns with o- have two forms : An autonomous form and a bound form. The autonomous version, the form with o-, becomes a bound form when o- is deleted.
3.3.1.1.	Deletion of the Initial Vowel
The initial vowel of Mao nouns is obligatorily dropped [a] when a genitival [one which is not morphologically marked [by zhü]] precedes [b] optionally in some cases, and obligatorily in others when words with deletable o- are added. This has two subclasses : [i] when the juxtaposed
3	This feature of theword-class of nouns has been noted for other Naga languages.
	Cf Kapfo 1989. One suspects this is true of most Naga languages at least in principle if not in detail.