neun
nine
The cardinal number that comes between eight and ten; the digit 9.
Das Buch hat neun Kapitel.
The book has nine chapters.

nine
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nine
The cardinal number that comes between eight and ten; the digit 9.
Das Buch hat neun Kapitel.
The book has nine chapters.

The adjective 'neunmalklug' (know-it-all) describes a person who thinks they know everything better than everyone else. It is derived from the number nine and is a common colloquial term.
Sei nicht so neunmalklug, du warst doch gar nicht dabei!
Don't be such a know-it-all; you weren't even there!
When describing a group of people, you can use the construction 'zu' + number + 't'. With 'neun' (nine), the form is 'zu neunt' (as a group of nine).
Wir waren gestern zu neunt im Kino.
There were nine of us at the cinema yesterday.
When 'neun' (nine) indicates a time, it is often used with prepositions such as 'um' (at), 'gegen' (around), or 'nach' (after). In spoken language, 'Uhr' (o'clock) is often left out.
Können wir uns morgen um neun treffen?
Can we meet tomorrow at nine?
ninth
'neun' and 'neunt' both belong to the number 9, but they are used differently. 'neun' is the regular number: you use it to count things or to say the time, nine o'clock. 'neunt' is an ordinal number and shows a position in a sequence, for example ninth place or the ninth day. Learners may confuse the forms because they look very similar. Remember: 'neun' answers 'How many?' or 'When?' for the time; 'neunt' answers 'Which number in the sequence?'.

Der Termin beginnt um neun, deshalb gehe ich früh los.
The appointment starts at nine, so I’m leaving early.
Sie ist beim Lauf als Neunte ins Ziel gekommen.
She crossed the finish line ninth in the race.