Translation

mūsu means "Moose" in English.
It's a katakanization, a loan-word.

mūsu is normally written with katakana, as ムース.
mūsu written with hiragana is むーす.
mūsu does not have kanji.
Romaji muu su
Katakana
Hiragana

Orthography Notes

Further Reading

Wikipedia: ヘラジカ (Moose)