急于
jíyū · HSK 7
anxious to
⏰ 急 = urgent/hurried + 于 = to/at; together: in a rush to do something
急 carries the hurried, anxious feeling; 于 is a function word marking what the urgency points toward. So 急于 = being in a hurry toward an action, i.e. eager or desperate to do it.
急 — heart radical 心 + 及 (reach)
A semantic-phonetic compound: the heart radical 心 supplies the meaning (an emotional state) while 及 ('to reach, catch up') gives the sound. Originally it depicted a racing, anxious heart — hence the modern senses 'urgent,' 'hurried,' and 'impatient.'
于 — two horizontal strokes 二 + vertical hook 亅
于 originated as a pictograph of breath or sound flowing outward, depicting exhalation through a passage. In oracle bone script it resembled a curved line showing motion or extension. Over time it became a grammatical preposition meaning 'at,' 'in,' or 'to,' losing its original concrete sense.