Translation

The Japanese word for "Reindeer" is tonakai トナカイ.

Romaji to na ka i
Hiraganaとなかい
Katakanaトナカイ
Kanji 馴鹿
Meaning Tamed Deer
School Level ✕, 中

Loan-word

The word "Reindeer" katakanized would be reindhia レインディア.
Romaji re i n dhi a
Katakanaレインディア
Hiraganaれいんでぃあ
Meaning Rein Deer

Trivia

Synonyms

Scientific name: Rangifer tarandus.

Further Reading

Wikipedia: Reindeer (トナカイ)