Picture a ship lying beside you: not the narrow bow, not the stern, but the long flat face in between — the broadest side it has. Broad plus side says exactly that. Everything else in the word can be seen growing out of that face: the row of guns set along it, the roar when the whole row at once, the burst of criticism that lands the same way, and the plain idea of being turned, or hit, on the long side instead of the front.
The packet's Wiktionary entry gives only the make-up of the word: 'From broad + side.' It does not trace how each later use appeared. So the links drawn above are offered as a way of holding the word together, not as a history of it.
手上的 Wiktionary 資料只寫了這個字的組成：broad + side。它沒有交代後來各個用法是怎麼一步步出現的。所以上面畫的那些連結，是幫助你把這個字握在一起的線索，不是歷史考證。
Wiktionary, entries for broadside (noun/adv/verb): 'From broad + side.'; packet source_ref kaikki:3f6f69a190036ae4:869029639
Three branches
最長的那一面
這一族就是核心本身：先是船身那片最長的臉，接著是「這一面朝著誰」，最後是「撞上的正是這一面」。
noun · C2
On a ship, the whole of one side of the hull above the water: the long flat face you see when a ship lies beside you. On old warships this was where the guns stood in a row.
舷側（船身水面以上的側面）
一整排砲齊射，和它借出去的火力
大砲就排在船身最長的那一面上，所以「那一面」順勢變成「那一排砲」，再變成「那一排砲同時開火」。這一族是核心畫面再往前走一步。
noun · C2
An attack in which all the guns along one side of a warship are fired at the same moment. It comes from the days of sailing warships, so you meet it mostly in history writing and in sea stories.
（軍艦）舷側齊射
只印一面的大張紙
這一族跟船沒有關係。它跟核心的連結只在 broad + side 這個組成上：用寬闊的那一面來印。資料沒有交代這個用法怎麼出現，所以這條線先當成記憶的線索，不當成歷史。
noun · C2
A large sheet of paper printed on one side only and then folded. Broadsides carried news, public notices, poems, or the words of a song, and today they are mostly seen in libraries, museums and old collections.
單面印刷的大張印張