Amiable means good-natured and likable. It’s usually used to describe people. Amicable means characterized by goodwill. It describes relationships or interactions between people. So, for instance, two amiable people might share an amicable friendship.
Both amiable and amicable are derived from the Latin amicabilis, meaning friendly, but amiable came to English via French. The adjectives were originally synonymous, but they have diverged in modern usage.
Examples
These writers use amiable correctly:
An amiable fellow, Wally committed this historic act on April 14, 2003 quite by accident. [American Spectator]
He’s amiable in a familiar Midwestern way, his disposition varies between cheerfully earnest and wry, and he uses words like “gosh.” [Wall Street Journal]
The amiable, shambling bears are also diplomats. [Los Angles Times]
And these writers correctly use amicable to describe relations or interactions between people or groups—for example:
No one wants to see this fun end, which is why the current labor negotiations are more amicable than they’ve been in the past. [Boston Globe]
Despite the earnest desire of many of the delegates to find an amicable solution to the growing crisis, the stated mission of the conference was doomed from the start. [Washington Post]
But it would appear hopes for an amicable divorce were misguided, as Reid has apparently demanded £6million in their divorce settlement, while Price had planned to give him £700,000. [Metro]
