Cannot go out leaving the child inside - not I (9)

I believe the answer is:
consonant
'i' is the definition.
Both the definition and answer are adjectives. Maybe you can see an association between them that I can't see?
'cannot go out leaving the child inside' is the wordplay.
'go out' indicates an anagram.
'leaving the child' becomes 'ons' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'inside' indicates putting letters inside.
'cannot' anagrammed gives 'conant'.
'conant' enclosing 'ons' is 'CONSONANT'.
'not' is the link.
Can you help me to learn more?
(Other definitions for consonant that I've seen before include "Letter; harmonious chord" , "B, C, D or F, perhaps?" , "One of several characters" , "In agreement" , "Speech sound, not a vowel" .)
