Seal plus -er gives you whatever does the . Picture something with a way in — the tiny holes in a concrete floor, the open top of a bag, an unstamped document, a game that is still winnable — and then picture the thing that closes it: a liquid, a machine, a person with a stamp, one late goal. English lets the -er point at a material, a tool or a human being without changing shape, which is why one small word covers so many different objects.
Formed from seal plus the ending -er, which names the thing or person that does the action.
由 seal 加上字尾 -er 組成，-er 指的是「做那個動作的東西或人」，所以字面上就是「封東西的那個」。
Wiktionary entry for sealer (etymology 1), etymology_text supplied in this packet: From seal + -er.
Three branches
把東西封起來的材料、機器或人
這一家直接就是核心畫面：seal + -er = 封東西的那個。差別只在那個「東西」是塗料、機器還是人。
noun · B2
A liquid you brush or spray onto a surface such as wood, concrete or stone, which dries into a thin layer that keeps out air, water and dirt; it is also used under paint so that a thirsty surface does not soak the paint up.
（表面用的）封層、底漆
把比賽結果封死的那一球
被封住的不是表面也不是袋口，而是比賽的結果：那一球進了，對手就再也打不開。屬於同一個畫面的比喻延伸，不是另一條字源。
noun · C1
In sports talk, a goal, point or shot scored so close to the end of a game that the losing side can no longer score enough to catch up.
（運動）鎖定勝局的那一球
獵海豹的人或船
這一支跟「封起來」沒有關係。它的 seal 是海豹那個字，只是拼法和唸法剛好一樣，所以不要硬把它接回核心畫面。
noun · C1
A person who hunts seals, or the ship that such hunters sail in.
獵海豹的人；捕海豹船