The Word is:”at”

at

at1
/at,ət/
preposition
preposition: at

1.expressing location or arrival in a particular place or position.
“they live at Conway House”
used in speech to indicate the sign @ in email addresses, separating the address holder’s name from their location.
2.expressing the time when an event takes place.
“the children go to bed at nine o’clock”
(followed by a noun without a determiner) denoting a particular period of time.
“the sea is cooler at night”
(followed by a noun without a determiner) denoting the time spent by someone attending an educational institution or workplace.
“it was at university that he first began to perform”
3.denoting a particular point or level on a scale.
“prices start at £18,500”
referring to someone’s age.
“at fourteen he began to work as a postman”
4.expressing a particular state or condition.
“his ready smile put her at ease”
expressing a relationship between an individual and a skill.
“boxing was the only sport I was any good at”
5.expressing the object of a look, thought, action, or plan.
“I looked at my watch”
expressing the target of a shot from a weapon.
“they tore down the main street, firing at anyone in sight”
expressing an incomplete or attempted action, typically involving repeated movements.
“she clutched at the thin gown”
6.expressing the means by which something is done.
“holding a prison officer at knifepoint”

Source credit: Google