孤独
gūdú · HSK 6
lonely
孤 (orphan) + 独 (alone) = lonely, solitary
孤 means orphan or solitary; 独 means alone or single. Together they stack two near-synonyms to intensify the sense of being utterly alone. 独 also appears in 单独 (alone) and 独立 (independent).
独 — dog radical 犭 + 蜀 (phonetic)
A semantic-phonetic compound: 犭 (dog) gives the meaning, since dogs were thought to fight when kept together and so were often kept singly, while 蜀 supplies the sound. The original sense was 'solitary dog,' which broadened to 'alone, single, only.'