GG5 leads with "unpleasant; disagreeable" but I agree they are a bit tame. The other JEs don't have them.
I don't think we need to be given examples for ominous.

@@ -28 +28 @@
-<gloss>ominous (e.g. dream)</gloss>
+<gloss>ominous</gloss>
@@ -29,0 +30 @@
+<gloss>unlucky</gloss>

https://context.reverso.net/translation/japanese-english/忌まわしい

sankoku 忌むべき (we give "abominable; detestable")
憎むべき　（"to hate", "to detest"）

E->J example defining "ominous" using 忌まわしい
忌まわしい を英語で教えて!
2023/01/16 10:00
古代，人の死は忌まわしいもとして、忌み嫌われてきたと言いたいです。
https://nativecamp.net/heync/question/20963


https://dictionary.goo.ne.jp/word/en/忌まわしい/
〔胸の悪くなる〕disgusting, detestable；〔不吉な〕ominous

The kanji itself currently has "abhor" attached to it.  

"abhorrent" is quite common:
https://context.reverso.net/translation/japanese-english/忌まわしい#abhorrent

abominable is also common.

"unpleasant" seems like quite an understatement. Does not appear in reverso (and there are many examples).  Same for "disagreeable" (very mild). 

"unsavory" likewise. "unsavory" is an actual attempt to downplay the severity of the term.  忌まわしい seems to be rather overtly severe

eow.alc.co.jp has a good list of terms; they are all severe, and "unsavory", "unpleasant", "disagreeable" do not appear on it.
https://eow.alc.co.jp/search?q=忌まわしい

+[rare] on [2].  Sense[2] does not appear in sankoku, and none of the glosses listed under [2] ever appear in reverso.
daijs give ~夢 as its example:

忌まわしい夢	67 ngrams

I'd say the absence from sankoku is telling.

for comparison to sense [1]:
忌まわしい記憶	7914  
忌まわしい事件	7698	  
忌まわしい過去	7582	  
忌まわしい出来事	2574

daijs defines sense[2] using  不吉.  We don't have "unlucky" on that term, I don't think it fits here either. Overly generic.  "An ominous dream" works, "An unlucky dream" does not. There's something associated with revulsion even in sense[2], not just "good luck/bad luck", I think.

@@ -18,2 +18 @@
-<gloss>unpleasant</gloss>
-<gloss>disagreeable</gloss>
+<gloss>abhorrent</gloss>
@@ -20,0 +20 @@
+<gloss>detestable</gloss>
@@ -22 +22,2 @@
-<gloss>unsavory</gloss>
+<gloss>horrid</gloss>
+<gloss>repugnant</gloss>
@@ -26 +27,2 @@
-<gloss>unlucky</gloss>
+<misc>&rare;</misc>
+<gloss>ominous (e.g. dream)</gloss>
@@ -28 +29,0 @@
-<gloss>ominous</gloss>

gg5, prog

@@ -27,0 +28 @@
+<gloss>ominous</gloss>