由于
yóuyú · HSK 3
owing/due/thanks to
由 = from/cause + 于 = at/in; together: 'caused by, owing to'
由 marks the source or reason of an action; 于 is a classical preposition meaning at/in/to. Stacked, 由于 introduces the cause of something, like English 'owing to' or 'due to'.
由 — pictograph of a gourd or vessel with a stem
由 originated as a pictograph showing a gourd, fruit, or vessel with a sprout or stem emerging from the top. Over time the meaning shifted abstractly to 'come forth from' or 'origin', giving modern senses like 'reason', 'cause', and 'from'. It is unrelated to 田 despite the visual similarity.
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.