Definition of aider in US English:

aider

noun

  • A person who, or thing which, provides aid or assistance; a helper; a help, support, or means of assistance. In later use especially in "aider and abettor".

Origin

Late 15th century; earliest use found in William Caxton (1415x24–1492), printer, merchant, and diplomat. From aid + -er.

Pronunciation

aider

/ˈeɪdə/