What does the cryptic crossword clue "Almost perfect notion (4)" mean?

The definition is "notion". The wordplay uses charade, deletion. IDEAL (synonym of "perfect") [curtailing: "Almost"]; definition: "notion" The answer is IDEA.

Almost perfect notion (4)

Guardian #3955 | 6 Across | 2022-07-31 flower

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Daily Mail Cryptic #16964 (2022-11-09)