A dictionary of Confusable Phrases: More Than 10,000 Idioms and Collocations

at a stroke • at the stroke
at a stroke —suddenly and with a single action or effort:
Some companies were in trouble because Mr. Heath changed
strategy at a stroke.
at the stroke —at exactly the time stated or agreed upon: We
agreed to meet for lunch, and he arrived at the stroke.
at a time • at one time
at a time —
1
. simultaneously: We present items, three at a
time, and ask informants to pick the one that is most different
from the other two. 2. is used of a particular period of time:
She grew up in the capital at a time when its artistic life was
at its most brilliant.
Note: 
The expression does not correlate in meaning with the
phrase at times— now and then: Our work is cut out for us,
even though it can be heartbreaking at times.
at one time —
1
. = at a time 
1
: Let’s start the dance again, all
at one time. 2. at some time in the past: At one time most
school teachers were men.
at a walk • in a walk
at a walk —at the ordinary gait: He watched her as she went
past at a walk.
in a walk —(coll.) 
1
. quickly and without much thought: If
you bother me too much, I’ll leave you in a walk! 2. easily and
without effort: Sunday is election day, and Viktor Yushenko
is expected to win in a walk.
at a white heat • in a dead heat
at a white heat—in a state of intense or extreme emotion: I
saw him once while at a white heat of vexation in the library
of the White House.
in a dead heat—(of a race, etc.) finishing at practically the
same time: The horses came to the finish in a dead heat, and,
without a photograph, the results were too close to call.
See also: at a heat / in heat.
at a word • in a word
at a word —following the word of command: At a word
from the guard they all splashed into the water and washed
their faces thoroughly.
in a word —(introductory or parenthetical) briefly; in short:
Another morning came, but no wife. In a word, she was never
heard of more.