абсолютный нуль - an absolute nothing: “He won’t be able to settle this problem. He is an absolute nothing.”
Авгиевы конюшни - the Augean stable: a very dirty place that had to be cleaned before the work can be done.
Адамово яблоко - an Adam’s apple: “ He is a funny-looking man, thin as a wire, and with an Adam’s apple, that looked as big as turkey egg.”
альфа и омега - alpha and omega: the beginning and the end. These are the first and the last letter in the Greek alphabet.
ангел-хранитель - a guardian angel: “My neighbour helps so much without expecting anything in return; he has been a true guardian angel.”
анемический характер - an anaemic character: a weak, subdued character
Ахиллесова пята - Achilles’ heel / the heel of Achilles (the one and only weakness but a fatal one): “John could have become an excellent musician today, had it not been for his gambling - his Achilles’ heel.”