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seacaidjacketfeminine noun
the
an t-seacaid
after a preposition
an t-seacaid
of the
na seacaide
plural
seacaidean
the (plural)
na seacaidean

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. Checked by a fluent speaker.