Derivative Nouns in Irish are _personal_ or _abstract_.
Personal Nouns end in _ōir_, _aire_, _ai_, _aid́_, and are produced from
primitive nouns, or past participles.
The terminations _ōir_, _aire_, are supposed to be broken forms of
the word _fear_, pronounced _fär_, a man. If so, then _fear_ must be
considered as the root of the Latin ending _or_, and of the English
suffix _er_.
Abstract Nouns terminate in _as_ or _eas_, masculine; in _aćt_, feminine;
or in the genitive case singular feminine of adjectives.
Diminutives are formed from nouns and adjectives, and end in _an_,
masculine; in _în_, masculine or feminine; in _ōg_, feminine.
Many words that are not diminutives end in _an_.
Other words terminating in _an_, from _tan_, time, or from _tain_,
possessions, are of this class. _Iat́_, a region, a territory, is, in its
fragmentary form _ia_, the termination of almost all the Latin names of
places that have that ending.
From the active signification of the ending _ać_, and from the meaning of
the term _neać_, an individual, an agent, of which _ać_ is apparently a
mere fragment, adjectives with this suffix become personal nouns, and as
such are expressive of office, action, or individuality.