at a moment—at one point in time (out of many):
At a heat vs In heat
at a heat—(coll.) at a single intense effort or action:
Auditory vs Acoustic vs Acoustical
Auditory, acoustic, acoustical mean of or relating to the hearing of sounds.
Arctic vs Artic
Always use arctic, not artic, as in Arctic Circle.
At a good price vs At a goodly price
at a good price—1. sell at a fairly high price:
Attraction vs Affinity vs Sympathy
Attraction, affinity, sympathy are comparable when they denote the relationship between persons or things that are involuntarily or naturally drawn together and exert, to some degree, an influence over each other.
Arcane vs Archaic
Arcane means mysterious or clearly understood by just a few.
At a glance vs At first glance
at a glance—notice smth. immediately without having to look carefully:
Attract vs Allure vs Charm vs Fascinate vs Bewitch vs Enchant vs Captivate
Attract, allure, charm, fascinate, bewitch, enchant, captivate mean to draw another by exerting an irresistible or compelling influence over him.
Arc vs Ark
Arc refers to something shaped with a curved or bowed line.
At a draft vs On draft
at a draft—drink all of smth. during one continuous action of swallowing:
Arbiter vs Arbitrator
These words are synonyms.