plain-island
All of the historical evidence for this placename points to Maighnis as the modern Irish form of this name.
Early seventeenth century examples include 'Moynish' (1613), 'Moynish' (1618), and 'Meynish' (1620). In the 17th and 18th centuries the placename is generally spelt 'Moynish'. These spellings are recorded in Latin or English documents and are transliterated spellings of the Irish name as it was then pronounced. Therefore since the early 17th century we can be fairly certain that the name was pronounced much as it is today.
When the Ordnance Survey was engaged in preparing its six-inch survey of Co. Kerry in 1841, Irish scholars were employed to collect the Irish names in the locality. Minish was recorded as Maighnis in Irish and translated as ‘plain of the island’ in the Ordnance Survey Namebook (Killarney Parish). Maighnis is a compound name which comes from *Magh-inis, literally meaning ‘plain-island’. In the 20th century the Irish spelling 'Magh Inis' was sometimes used. It is important to note that this form is grammatically incorrect and inadmissible in Irish. If the placename consisted of two separate words, the word inis would be in the genitive case (an tuiseal ginideach) after Magh / Maigh, giving Ma(i)gh Inse. However, there is no evidence whatosever to support that particular structure as regards the present placename.
Maigh-inis was recommended by the author ‘An Seabhac’, Pádraig Ó Siochfhradha, who wrote two books about Kerry placenames. The last-mentioned spelling of the name is preserved on one of the index cards of Kerry placenames written by An Seabhac and held in our office.
One can compare Maighnis in Co. Kerry to the placename Maínis in the Conamara Gaeltacht which is of the same origin—the only difference being that in the latter district a long i-vowel, í [iː], is used in the first syllable of the name.