Meaning : Without advance planning.
Example :
They met accidentally.
Synonyms : by chance, circumstantially, unexpectedly
With intention. In an intentional manner.
He used that word intentionally.Meaning : Of a minor or subordinate nature.
Example :
These magnificent achievements were only incidentally influenced by Oriental models.
Synonyms : incidentally
Meaning : Without intention. In an unintentional manner.
Example :
She hit him unintentionally.
Synonyms : unintentionally
With intention. In an intentional manner.
He used that word intentionally.