I. -er¹ /ə $ ər/ suffix
forms the comparative of many short adjectives and adverbs:
hot, hotter
dry, drier
fast, faster
⇒ -est

[TahlilGaran] Dictionary of Contemporary English ▲

II. -er² suffix [in nouns]

1. someone who does something or is doing something:
a dancer
a driver

2. something that does something:
a scraper (=a tool you use for scraping)
⇒ -ar, -or

[TahlilGaran] Dictionary of Contemporary English ▲

ER /ˌiː ˈɑː $ -ˈɑːr/ noun [countable usually singular] American English informal
emergency room

[TahlilGaran] Dictionary of Contemporary English ▲

er /ɜː, ə $ ɜːr, ər/ interjection British English
[Date: 1800-1900; Origin: A representation of the sound]
a sound you make when you do not know exactly what to say next:
Well, er – I’m not really sure.

[TahlilGaran] Dictionary of Contemporary English ▲

ER
Emergency Room - the place in a hospital which deals with emergency situations
The victims of the accident were quickly taken to the ER.

[TahlilGaran] English Idioms Dictionary ▲