Question

Which of our digits is definitely odd, but as a word it Is mostly even (1-9)

Answer 1

one- 3 letters 
three- 5 letters 
five- 4 letters 
seven- 5 letters 
nine- 4 letters

both 5 and 9 are odd numbers with 4 letters in the word

Answer 2

Ohhh !  I get it !

The digit you're talking about is ' 7 '.  ( seven )