Picture a man with one line of work that feeds him, and a doorway. On one side of the door he has goods to hand over; on the other side he has tools and a skill in his hands. Either way, what he 'has' is a trade, and the whole word is just that: trade plus man, the man who lives by it. English keeps both halves of trade alive — the buying-and-selling half and the learned-skill half — so the same word lands on a in one country and on a in another.
From the word’s history
Wiktionary gives tradesman as trade + -s- + -man, literally 'man of a trade'. The word itself does not choose which meaning of trade is meant, which is why the modern uses split the way they do.
依 Wiktionary 的說明，tradesman 是 trade 加上連接的 -s- 再加上 -man，字面上就是「有一門 trade 的男人」。這個字本身沒有替你決定 trade 是「買賣」還是「手藝」，這正好說明了它今天為什麼會分成兩邊。也請注意 -man 這個字尾指的是男性。
Wiktionary entry for tradesman, etymology_text in this packet (kaikki:3f6f69a190036ae4:1135538075:11109)
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