noun
weasel; Japanese weasel
Typically refers to the Japanese weasel (Mustela itatsi), but can be used for weasels in general. Common in everyday language.
イタチが庭に現れた。
A weasel appeared in the garden.
イタチは小さい動物を捕まえる。
Weasels catch small animals.
noun
mustelid
Broader biological sense: any member of the family Mustelidae, including weasels, badgers, otters, etc. More technical than sense 1.
イタチ科にはカワウソやアナグマも含まれる。
The mustelid family includes otters and badgers.
Rarely used kanji form.
The word いたち is of native Japanese origin. The kanji 鼬 is a Chinese character adopted for its meaning, but the reading is not derived from Chinese. The exact etymology is uncertain.