An Aid

1. (uncountable) Help; assistance; succor, relief.
2. (countable) A helper; an assistant.
3. (countable) Something which helps; a material source of help.
4. (countable, Britain) An historical subsidy granted to the crown by Parliament for an extraordinary purpose, such as a war effort.
5. (countable, Britain) An exchequer loan.
6. (countable, law) A pecuniary tribute paid by a vassal to his feudal lord on special occasions.
7. (countable) An aide-de-camp, so called by abbreviation.