A1 immediately after the first and before any others:

A1 the position in which a person finishes a race or competition if they finish immediately behind the winner:

B1 Second is used to show that only one thing is better, bigger, etc. than the thing mentioned:

B1 another:

happening only once out of every two possible times:

B1 after the first and before any others:

B2 also secondly used to introduce the second thing in a list of things you want to say or write:

A2 [ C ] abbreviation sec., s a short unit of time that is equal to a 60th of a minute:

B1 [ C ] a very short period of time:

[ S ] the second person or thing to do or be something, or the second person or thing mentioned:

[ C ] specialized mathematics the smallest unit used for measuring an angle:

C2 [ C ] a product that is sold cheaply because it is damaged or not in perfect condition

[ C ] a person who takes care of someone who is fighting in a boxing competition or, in the past, in a duel (= organized fight)

[ U ] also second gear in a vehicle, the gear that combines power with limited speed and is used when increasing or reducing speed:

[ C ] UK also second-class degree an undergraduate degree from a university in the UK and some other countries that is a good degree but not the best possible

[ C usually singular ] informal →  second base

to make a formal statement of support for a suggestion made by someone else during a meeting so that there can be a discussion or vote:

to send an employee to work somewhere else temporarily, either to increase the number of workers or to replace other workers, or to exchange experience or skills: