Cases of word usage

1) an additional (another)

2) giving additional help or support (auxiliary)

3) the act of extending or being extended; an additional part (extension)

4) (a) detailed study or investigation to discover new facts, get additional information etc (research)

5) kept for use when needed; additional to what is being or will be used; a spare part (for a machine or engine); (to agree) to avoid hurting, punishing, destroying, (a person, building etc) (spare)