As an adjective, through means finished or done. As an adverb it can mean backward and forward, completely, up to and including, or all the way to the end. The preposition through means in and out of.

Through has lots of meanings. If you finished your homework you might shout — gleefully — "I'm through!" Those people who wouldn't be quiet talked through the entire movie. The first half of the alphabet are the letters A through M. If you've memorized the multiplication table, you know the whole thing through. And, of course, you walk through a door.

Definitions of through

adj having finished or arrived at completion

“after the treatment, the patient is through except for follow-up”
“almost through with his studies”
done, through with
ended or brought to an end

adj (of a route or journey etc.) continuing without requiring stops or changes

“a through street”
“a through bus”
through traffic”
direct in spatial dimensions; proceeding without deviation or interruption; straight and short

adv from beginning to end

“read this book through

adv over the whole distance

“this bus goes through to New York”

adv to completion

“think this through very carefully!”

adv throughout the entire extent

“got soaked through in the rain”
“I'm frozen through
“a letter shot through with the writer's personality”
“knew him through and through”
“boards rotten through and through”
through and through

adv in diameter

“this cylinder measures 15 inches through

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