Learn Arabic (Modern Standard): هو المشارك الثامن.

In Arabic, ordinal numbers (like first, second, eighth) act like adjectives. They come after the noun they describe and must match it. Because المشارك (the participant) is definite (it has ال), the word الثامن (eighth) must also take ال to match it.

Where is the word for "is" in this Arabic sentence?

Arabic does not use a word for "is" or "are" in present tense sentences. By putting the pronoun هو (he) right before the noun phrase المشارك الثامن (the eighth participant), the "is" is naturally understood.

How is الثامن (eighth) related to the regular number eight?

They share the same core consonant sounds. Regular numbers tell you how many, but ordinal numbers tell you the order. To make an ordinal number from 2 to 10, Arabic shapes those root letters into a specific rhythm or pattern. That is why ثمانية (eight) transforms into ثامن (eighth).

What would this sentence look like if the participant was a woman?

Since ordinal numbers act as adjectives, they must match the noun in gender. "She" is هي and a female participant is المشاركة. You would also add the feminine ending to "eighth", making the sentence: هي المشاركة الثامنة.