al‧ly1 W3 plural allies [countable]
a country that agrees to help or support another country in a war:
a meeting of the European allies
the group of countries including Britain and the US that fought together in the First and Second World Wars
someone who helps and supports you when other people are trying to oppose you:
Ridley was one of the Queen's closest allies.
a staunch ally (=very close ally) of President Soares
a network of political allies
She knew she had found an ally in Ted.
something that helps you succeed in a difficult situation:
Exercise is an important ally in your campaign to lose weight.