weasel; Japanese weasel
Typically refers to the Japanese weasel (Mustela itatsi), but can be used for weasels in general. Common in everyday language.
A weasel appeared in the garden.
mustelid
Broader biological sense: any member of the family Mustelidae, including weasels, badgers, otters, etc. More technical than sense 1.
The mustelid family includes otters and badgers.
Weasels catch small animals.
イタチ (weasel) keeps its brown coat year-round, whereas オコジョ (stoat) turns white in winter.
counter for small animals · counter for rolls of cloth · archaic counter for horses · roll of cloth
going round in circles; game of cat and mouse; pointless back-and-forth · itachi-gokko; Edo-period children's hand game
mongoose
whirlwind cut; vacuum cut in the skin · mythical weasel-like creature riding whirlwinds
false indigo; bastard indigo; leadwort
goatsbeard brotula
Katakana spelling is common for animal names; usually written in kana.
Kanji form is rare and mainly encountered in literary or scientific contexts.
Hiragana spelling is also used, though katakana is more typical for animals.
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.