To keep something secret.
Mantener algo en secreto. (Mantener algo en secreto.)
"I’ll tell you a secret, but keep it under your hat."
"Te diré un secreto, pero mantenlo en secreto." (Te diré un secreto, pero **manténlo en secreto**.)
to suddenly realize the solution to a problem
To retire someone or something from active use.
to reassure someone that they can handle a situation
To do everything possible to achieve something.
A source of endless complications or trouble.
to become difficult to control