1 words in this vocabulary list
noun A cog is a toothed wheel or bar that engages with another toothed part to transmit motion in a machine.
preposition In this phrase, 'in' is a preposition that shows the relationship between 'cog' and 'machine'.
article The articles 'a' and 'the' are used before 'cog' and 'machine' to indicate that they are singular nouns.