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eaglaischurchfeminine noun
the
an eaglais
after a preposition
an eaglais
of the
na h-eaglaise
plural
eaglaisean
the (plural)
na h-eaglaisean

Every form but the headword, the genitive and the plural is worked out by the spelling rules in the grammar guide, so what you see here is what the guide teaches. Awaiting a fluent speaker’s review.