At sixes and sevens

a cardinal number, five plus one.
a symbol for this number, as 6 or VI.
a set of this many persons or things.
a playing card, die face, or half of a domino face with six pips.
Cricket. a hit in which the ball crosses the boundary line of the field without a bounce, counting six runs for the batsman.
Compare (def 3).
an automobile powered by a six-cylinder engine.
a six-cylinder engine.
amounting to six in number.
at sixes and sevens,

in disorder or confusion.
in disagreement or dispute.

noun
the cardinal number that is the sum of five and one See also number (sense 1)
a numeral, 6, VI, etc, representing this number
something representing, represented by, or consisting of six units, such as a playing card with six symbols on it
Also called six o’clock. six hours after noon or midnight
(cricket) Also called sixer

a stroke in which the ball crosses the boundary without bouncing
the six runs scored for such a stroke

a division of a Brownie Guide or Cub Scout pack
at sixes and sevens

in disagreement
in a state of confusion

(informal) knock someone for six, to upset or overwhelm someone completely; stun
six of one and half a dozen of the other, six and two threes, a situation in which the alternatives are considered equivalent
determiner

amounting to six: six nations
(as pronoun): set the table for six

noun
Les Six (le). a group of six young composers in France, who from about 1916 formed a temporary association as a result of interest in neoclassicism and in the music of Satie and the poetry of Cocteau. Its members were Darius Milhaud, Arthur Honegger, Francis Poulenc, Georges Auric, Louis Durey, and Germaine Tailleferre
n.

Old English siex, six, sex, from Proto-Germanic *sekhs (cf. Old Saxon and Danish seks, Old Norse, Swedish, and Old Frisian sex, Middle Dutch sesse, Dutch zes, Old High German sehs, German sechs, Gothic saihs), from PIE *s(w)eks (cf. Sanskrit sas, Avestan kshvash, Persian shash, Greek hex, Latin sex, Old Church Slavonic sesti, Polish szesc, Russian shesti, Lithuanian szeszi, Old Irish se, Welsh chwech).

Six-shooter, usually a revolver with six chambers, is first attested 1844; six-pack of beverage containers is from 1952, of abdominal muscles by 1995. Six of one and half-a-dozen of the other “little difference” is recorded from 1833. Six-figure in reference to hundreds of thousands (of dollars, etc.) is from 1840. Six feet under “dead” is from 1942.

Phrase at sixes and sevens originally was “hazarding all one’s chances,” first in Chaucer, perhaps from dicing (the original form was on six and seven); it could be a corruption of on cinque and sice, using the French names (which were common in Middle English) for the highest numbers on the dice. Meaning “at odds, in disagreement or confusion” is from 1785, perhaps via a notion of “left unsettled.”

In a state of confusion or disorder: “Trying to cram for this math test has me all at sixes and sevens.”

modifier

In a state of confusion and disorder

[1670+; fr the earlier phrase ”set on six and seven,” leave to chance, possibly a fanciful alteration of ”set on cinque and sice” (= five and six), a gambling term denoting hazarding everything on throwing a five and a six at dice]

verb phrase

To pay attention; become aware; wake up and smell the coffee: Let’s do something that’ll make him sit up and take notice (1889+)
Confused, disorganized, disorderly, as in We’ve just moved in, and the office is still at sixes and sevens, or The new college admissions tests were poorly explained, leaving the students at sixes and sevens. This ancient term is thought to come from a game of dice in which throwing a six or seven had a particular significance. The name of the game has been lost, but most likely betting on such a throw was very risky, denoting disorder and confusion. [ Late 1300s ]

six feet under
six of one, half a dozen of the other

also see:

at sixes and sevens
deep six
Joe six-pack