'second' is a noun that means a unit of time equal to one sixtieth of a minute. It is usually abbreviated to 'sec' and is written in numbers like '2 sec' or '3.5 sec'.
1. I had to wait for two seconds before the movie started.
2. I need to reduce the cooking time by a second.
3. The quantum entanglement lasted for 0.000000001 seconds.
when referring to a second in a fraction, use a hyphen to join the two numbers together (e.g. 'one-half second). When using the word second in scientific notation, you need to use an 'e' to indicate the exponent (e.g. 1.2e-6 seconds).
'second' is also used as an adjective to describe people or objects that are not the original versions or editions.
1. I bought a second-hand car that was in good condition.
2. The dressmaker creates beautiful, second dresses.
3. The copycat product is of poorer quality than the original.
for adjectival usage, a hyphen is not necessary when the word is placed before the noun or pronoun (e.g. 'second car'). However, when the word follows the noun it should be hyphenated (e.g. 'car second-hand').