忠于
zhōng yú · HSK 7
to be loyal to
🐕 忠 = loyal/faithful + 于 = to/toward; 忠 stacks 中 (center) over 心 (heart) — a centered heart
忠于 means to be loyal to. 忠 is 中 (zhōng, center) sitting on 心 (heart): a heart held to the center, steadfast. 于 (yú) is the grammar word for to or toward, naming the target of the loyalty.
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.