cog1

[kog, kawg] /kɒg, kɔg/
noun
1.
(not in technical use) a gear tooth, formerly especially one of hardwood or metal, fitted into a slot in a gearwheel of less durable material.
2.
a cogwheel.
3.
a person who plays a minor part in a large organization, activity, etc.:
He's just a small cog in the financial department.
verb (used without object), cogged, cogging.
4.
(of an electric motor) to move jerkily.
verb (used with object), cogged, cogging.
5.
to roll or hammer (an ingot) into a bloom or slab.
Idioms
6.
slip a cog, to make a blunder; err:
One of the clerks must have slipped a cog.
Origin
1200-50; Middle English cogge, probably < Scandinavian; compare Swedish, Norwegian kugg cog
British Dictionary definitions for slip a cog

cog1

/kɒɡ/
noun
1.
any of the teeth or projections on the rim of a gearwheel or sprocket
2.
a gearwheel, esp a small one
3.
a person or thing playing a small part in a large organization or process
verb cogs, cogging, cogged
4.
(transitive) (metallurgy) to roll (cast-steel ingots) to convert them into blooms
Word Origin
C13: of Scandinavian origin; compare Danish kogge, Swedish kugge, Norwegian kug

cog2

/kɒɡ/
verb cogs, cogging, cogged
1.
(slang) to cheat (in a game, esp dice), as by loading a dice
Word Origin
C16: originally a dice-playing term, of unknown origin

cog3

/kɒɡ/
noun
1.
a tenon that projects from the end of a timber beam for fitting into a mortise
verb cogs, cogging, cogged
2.
(transitive) to join (pieces of wood) with cogs
Word Origin
C19: of uncertain origin
Word Origin and History for slip a cog

cog

n.

c.1300, "cog wheel;" late 14c., "tooth on a wheel," probably a borrowing from a Scandinavian language (cf. Norwegian kugg "cog") and cognate with Middle High German kugel "ball."

Idioms and Phrases with slip a cog

slip a cog

Also, slip a gear or one's gears. Lose one's ability to reason soundly or make correct judgments, as in She must have slipped a cog or she would never have gone out barefoot in December, or What's the matter with him? Has he slipped his gears? These slangy usages allude to a mechanical failure owing to the cog of a gear or a gear failing to mesh. The first dates from about 1930, the variant from the 1960s.

cog

In addition to the idiom beginning with cog also see: slip a cog