second childhood

have second thoughts

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

just a second

A short period of time, typically anywhere from a few seconds to several minutes or more.

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 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.