What does "just short of amazing" mean?

[Hambo]

English Language Tests, Intermediate level

ESL/EFL Test #637 "English Slang Idioms (379)", question 3

"Your friend Jack sure said a ......... when he described you as attractive. You're a knockout!!" Tom exclaimed to Gina.

(a) handful
(b) mouthful
(c) spoonful
(d) thankful

English Language Tests, Intermediate level

ESL/EFL Test #637 "English Slang Idioms (379)", answer 3

"Your friend Jack sure said a mouthful when he described you as attractive. You're a knockout!!" Tom exclaimed to Gina.

Correct answer: (b) mouthful
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meaning of "just short of amazing"

[Kitosdad]

Fantastic. Unbelievably beautiful. A dream.
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