opossamu means "Opossum" in English.
It's a katakanization, a loan-word.

  • In some places, the words Possum and Opossum are synonymous. In other places, however, Possum refers to animals of the suborder Phalangeriformes while Opossum refers to animals of the order Didelphimorphia.
opossamu is normally written with katakana, as オポッサム.
opossamu written with hiragana is おぽっさむ.
opossamu does not have kanji.
Romaji o po ssa mu

Orthography Notes

  • ッサ contains a small tsu which makes the consonant of the syllable longer.

Further Reading

Wikipedia: オポッサム (Opossum)