Abstemious
Sparing in consumption, especially food & drink
Abtruse
Hard to understand
Abdicate
To give up, often in formal manner
Acerbic
sour; harsh
Accretion
an increase
Abeyance
a temporary suspension
Aberrant
unusual
Abjure
to give up, often in formal manner
Acme
the highest point
Acidulous
sour; sharp