The most common and most likely answer to this crossword clue is the 7 letter word NATURAL
I've seen this crossword clue in Financial Times
N
A
T
U
R
A
L
More clues leading to the result NATURAL
- Unforced, one may cancel a flat
- Logical person sure to succeed?
- Unrefined person sure to succeed
- Common brown climbing flower
- Note one that’s certain to be a success
- . An accidental certainty?
- Spontaneous Aunt travelled by rail wanting independence
- Rising brown river is untreated
- Ant scrambled up mountain without man’s involvement
- Effortlessly talented, score mark?
Buddy explains!

The straight part
We know that "Note/one that’s certain to be a success" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case note/one that’s certain to be a success = natural.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does NATURAL mean?
NATURAL noun- A native inhabitant of a place, country etc.
- A note that is not or is no longer to be modified by an accidental.
- The symbol ♮ used to indicate such a natural note.
- One with an innate talent at or for something.
- An almost white colour, with tints of grey, yellow or brown; originally that of natural fabric.
- One with a simple mind; a fool or idiot.
- One's natural life.
- A hairstyle for people with afro-textured hair in which the hair is not straightened or otherwise treated.
- Closed under submodules, direct sums, and injective hulls.
- That exists and evolved within the confines of an ecosystem.
- Of or relating to nature.
- Without artificial additives.
- As expected; reasonable.
- Neither sharp nor flat. Denoted ♮.
- Produced by natural organs, such as those of the human throat, in distinction from instrumental music.
- Applied to an air or modulation of harmony which moves by easy and smooth transitions, digressing but little from the original key.
- Having 1 as the base of the system, of a function or number.
- Without, or prior to, modification or adjustment.
- Having the character or sentiments properly belonging to one's position; not unnatural in feelings.
- Connected by the ties of consanguinity.
- Related genetically but not legally to one's father; born out of wedlock, illegitimate.
- (of sexual intercourse) Without a condom.
- Bidding in an intuitive way that reflects one's actual hand.
- Naturally; in a natural manner.