Okaikiar is a highly inflected language, and this shows up most dramatically in the nouns. Each noun changes form to show one of two numbers (singular and plural), nine cases, and three modes. There are three different declension patterns, each identified by a set of distinctive endings. To obtain the declined forms of the noun, this ending is removed, yielding the stem, to which other endings are added.
The nine cases are as follows:
| Case | Use |
|---|---|
| Nominative | Basic form of the word; used for the subject of verbs as well as words equated with the subject. |
| Accusative | Used for the direct object of transitive verbs. |
| Causative | Used to give the motive or reason behind an action. A noun in the causative is often translated into English using the preposition because. |
| Locative | A noun in the locative specifies a location where something else is happening. Often translated in English with the prepositions at or in, etc.. |
| Instrumental | A noun in the instrumental specifies the instrument used to perform an action, often translated via with or by means of. |
| Ablative | A noun in the ablative specifies the origin of some motion; often translated via from or out of. |
| Allative | A noun in the allative specifies the destination of some motion; often translated via to or toward. |
| Dative | A noun in the dative specifies the indirect object of a verb. |
| Genitive | A noun in the genitive specifies a belonging relationship, often translated via a possessive (-'s) or the preposition of. |
A noun in Okaikiar can be placed in one of three modes: the default mode, spatial mode, or temporal mode. In spatial or temporal mode the meaning of the noun is restricted to spatial or temporal senses. For instance, in the default mode, the locative case may refer to location in space or time, just as we may use at for either sense in English. But in spatial mode, the locative case can refer only to location in space, and in temporal mode the locative case can refer only to location in time.
The modes may alter the English gloss. For instance, the usual way of translating the English adverb here (meaning at this place) into Okaikiar is to put the personal pronoun zamo, meaning I, into the locative case, with or without changing the mode. To get the noun here (meaning this place), the pronoun is placed into the spatial mode. So the same word that means I in the default mode means here in spatial mode and now in temporal mode.
About 40% of all nouns are in the first declension, indicated by the nominative ending -ar. The paradigm is illustrated below using the word kaikiar (the root of Okaikiar), which means speech. Note in particular that there is no singular/plural distinction in the ablative, locative, or allative cases.
| Case | Singular | Plural |
|---|---|---|
| Nominative | kaikiar | kaikier |
| Accusative | kaikiard | kaikierd |
| Causative | kaikiur | kaikiyr |
| Locative | kaikiird | kaikiird |
| Instrumental | kaikiurd | kaikiyrd |
| Ablative | kaikiir | kaikiir |
| Allative | kaikiirk | kaikiirk |
| Dative | kaikiark | kaikierk |
| Genitive | kaikior | kaikiør |
The second declension also claims about 40% of Okaikiar nouns, split evenly between the two nominative endings -al and -an. The paradigm is illustrated using the words zodal, which means air, and ierzan, which means fire. Again, there is no singular/plural distinction in the locative cases, but in this declension that distinction is also missing from the causative and instrumental.
| Case | Singular | Plural | ||
|---|---|---|---|---|
| Nominative | zodal | ierzan | zodel | ierzen |
| Accusative | zodald | ierzand | zoded | ierzend |
| Causative | zod'l | ierz'n | zod'l | ierz'n |
| Locative | zodild | ierzind | zodild | ierzind |
| Instrumental | zod'ld | ierz'nd | zod'ld | ierz'nd |
| Ablative | zodil | ierzin | zodil | ierzin |
| Allative | zodelk | ierzenk | zodeilk | ierzeink |
| Dative | zodalk | ierzank | zodelk | ierzenk |
| Genitive | zodol | ierzon | zodøl | ierzøn |
Finally, about 20% of all nouns are in the third declension, indicated by the nominative singular ending -o. Borrowings from other languages are typically modified by adding -o, placing them into this declension. The paradigm is indicated using the personal pronoun zamo, which means I/me.
| Case | Singular | Plural |
|---|---|---|
| Nominative | zamo | zamø |
| Accusative | zamod | zamød |
| Causative | zamu | zamy |
| Locative | zamad | zamed |
| Instrumental | zamud | zamyd |
| Ablative | zama | zame |
| Allative | zamak | zamek |
| Dative | zamok | zamøk |
| Genitive | zame | zami |