Several parts combine into one character.

犬 is a side-view pictograph of a dog — a small head, an arched back, a tail curling upward. The character differs from 大 (big) by just a single dot, but their etymologies are unrelated despite the visual closeness. As a radical compressed into compounds, 犬 takes the form 犭 (the "beast-side" radical), generating the entire vocabulary of mammals: 狗 (gǒu, dog — modern Mandarin's everyday word), 猫 (cat), 猛 (fierce), 狂 (wild / mad), 獣 (beast).

Korean reading "gyeon." 愛犬 (aegyeon, beloved pet dog), 名犬 (myeonggyeon, pedigreed dog), 軍犬 (gungyeon, military dog), 盲導犬 (maengdogyeon, guide dog for the blind), 忠犬 (chunggyeon, loyal dog). In Korean conversation, dogs are nearly always referred to using the native word (gae), while Sino-Korean compounds use 犬.

Mandarin quǎn, 3rd tone — but here Mandarin made a striking historical lexical shift. The everyday Chinese word for "dog" today is 狗 (gǒu), not 犬. 犬 is reserved for formal compounds: 警犬 (jǐngquǎn, police dog), 军犬 (jūnquǎn, military dog), 牧羊犬 (mùyángquǎn, sheepdog), 猎犬 (lièquǎn, hunting hound). Spoken Mandarin always uses 狗 (gǒu) for the animal — the bare "dog" you might see on the street, in idioms, or in a Chinese zodiac. This is one of the cleanest formal-vs-colloquial register splits in CJK.

Japanese on-reading ケン (ken) — 愛犬 (aiken, beloved dog), 盲導犬 (mōdōken, guide dog), 野犬 (yaken, stray dog). Kun-reading いぬ (inu) — 犬 (inu, dog), 子犬 (koinu, puppy), 番犬 (banken, watchdog). The famous loyal Akita 忠犬ハチ公 (Chūken Hachikō, "Loyal Dog Hachikō") who waited at Shibuya Station for his dead owner uses the Sino-Japanese compound for added formal gravitas — even the statue's name elevates the dog to literary status.

Memory aid: a side-view dog with curling tail. One dot away from 大 (big) — keep them straight by remembering: the extra dot is the dog's loyal little spot.