Why is it “唾棄すべき” rather than just “唾棄”?

Question

I've come across a line in a work of fiction -

ただの唾棄すべき存在であった高橋家はここで終わりだ。

I am familiar with the use of ~べき which means "should do/ be a certain way"

But my vocabulary book and dictionary lists 唾棄すべき as a set phrase meaning "detestable; despicable; abhorrent​", but 唾棄 without the "すべき" means the same thing, so what's different when べき is added? Is it following the grammar rules of ~べき that something should be a certain way?

So, If I put it into a sentence in English would it be more accurate to say;

The Takahashi family who were simply abhorrent will cease here.

Or;

The Takahashi family who would have been simply abhorrent will cease here.

Answer 1

But my vocabulary book and dictionary lists 唾棄{だき}すべき as a set phrase meaning "detestable; despicable; abhorrent​",

You have a good dictionary, then.

but 唾棄 without the "すべき" means the same thing.

If that is what your dictionary says, I'll take back my comment above.

「唾棄」 is a noun. It simply could not mean "detestable; despicable; abhorrent​" even if you wanted it to. As a noun, it could not have an adjective-like definition.

「唾棄」 means "the act of detesting or hating". Its literal and original meaning is, as the kanji would suggest, "spitting out saliva". I am sure you can see a relationship between the two.

Both 「唾棄」 and 「存在{そんざい}」 are nouns and to connect the two nouns you need a word or two. 「すべき」 would be a natural choice here.

Literally, 「唾棄すべき存在」 is "the 存在 that should be 唾棄するed".

Finally, your first translation is closer to the original in terms of what the original sentence lterally means, but your second one is not bad at all, either. I suggest that you pick the one that you feel fits the context better.

Answer 2

Simply, 唾棄 without すべき is a suru-verb that means "to detest; to despise; to abhor." Thus 唾棄すべき naturally means "detestable; despicable; abhorrent​". 唾棄 on its own never servers as a (na-)adjective.

Looks like jisho's definition is a bit confusing, but I think an advanced learner who wants to learn difficult words like 唾棄 should try a monolingual dictionary and corpus. See 唾棄 on デジタル大辞泉.