A sentence with a line down the middle. On one side stands the thing you are talking about. On the other side is everything you say about it. Predicate is that second side — the said-about part.
From Medieval Latin praedicatum, the thing said of a subject, from praedicare (to proclaim), which is prae- (before) plus dicare (to proclaim). It is a doublet of preach.
來自中世紀拉丁文 praedicatum，意思是「被說在主詞身上的東西」，出自 praedicare（公開宣告），由 prae-（在前面）加 dicare（宣告）組成；它跟 preach 是同一個祖先分出來的。所以這個字從一開始就跟「把話說出來、說在某個對象身上」綁在一起。
Wiktionary etymology notes supplied in this packet (source_ref kaikki:3f6f69a190036ae4:153149332 and :153228357)
Three branches
句子裡說主詞怎麼了的那一半
最直接的落地：把那條中線畫進真正的句子裡。
noun · C1
In grammar, the predicate is the part of a sentence that tells you what the subject does or what the subject is. In 'Fish swim', the predicate is 'swim'; in 'She is an artist', it is 'is an artist'.
述語；謂語
把一個性質說在某個東西身上
把那條線從句子裡抽出來，變成一個動作：你拿起一個性質，把它安在某個對象身上。
verb · C2
To say that a quality or a fact is true of something: you predicate X of Y. In grammar it also means to make a word the predicate of a sentence, and in older writing it can simply mean to announce something publicly.
斷言（把某性質說在某物身上）
整件事靠哪一句話撐著
如果一句話被說在某件事身上，那件事就跟著那句話站或倒。這一步把「說在…身上」變成「建立在…之上」。
verb · C1
If a plan, decision, or argument is predicated on something, it is built on that thing being true. Take that thing away and the plan has nothing left to stand on.
以…為前提；建立在…之上