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seòmarroommasculine noun
the
an seòmar
after a preposition
an t-seòmar
of the
an t-seòmair
plural
seòmraichean
the (plural)
na seòmraichean

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.