just a second

have second thoughts

To change one's opinion, or be uneasy about a previous decision.

play second fiddle

To play a subsidiary or subordinate role to someone or something else.

second banana

A comedian who plays a secondary or supporting role, especially as straight man and traditionally in vaudeville or burlesque theatre.

second childhood

The period or state of cognitive decline of an elderly person, characterized by childlike judgment and behavior.

second fiddle

A sidekick or subordinate, or the role of such a person.

second gear

Mediocre, sluggish performance.

second nature

A mindset, skill, or type of behavior so ingrained through habit or practice that it seems natural, automatic, or without a basis in conscious thought.

second string

Not as good; of a lower quality or condition.