One way to hold this word: stand on a path and look up at a rock that does not stop at the cliff face but carries on out, over your head, with nothing underneath it. Two things make the picture — an edge, and a part that goes past the edge instead of stopping there. Everything the word does comes from that one shape: the going-past itself, the piece that goes past, how far it goes, and the feeling of something sitting above you that you cannot get out from under.
From the word’s history
Wiktionary gives Old English oferhangan, that is over- plus hang. The word is still doing exactly what its two parts say: something hangs over something else.
字典說 overhang 來自古英語 oferhangan，也就是 over-（在……上方）加 hang（懸掛）。這個字到今天還完全照著這兩個部分在運作：一樣東西懸在另一樣東西的上方。
Wiktionary via kaikki extract, source_ref kaikki:3f6f69a190036ae4:203790980 ('From Old English oferhangan, corresponding to over- + hang')
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