bottom · noun /ˈbɒt.əm/Full view
bottom (LOWEST PART)
A1 C usually no plural the lowest part of something
Dictionary examples:

He stood at the bottom of the stairs and called up to me.

Extra information can be found at the bottom of the page.

Learner example:

One of the most amazing places we visited was a small lake at the bottom of a huge mountain. (Preliminary English Test; B1; Spanish)

A2 C usually no plural the flat surface on the lowest side of something
Dictionary example:

There was a label on the bottom of the box.

Learner example:

On the bottom of the box I found a card saying "MARRY ME... (Preliminary English Test; B1; Georgian)

A2 no plural the lowest position in a group, organization, etc.
Dictionary example:

At school, Einstein was at the bottom of his class.

B1 no plural the ground under a river, lake, or sea
Dictionary example:

The ship had sunk to the bottom of the sea.

Learner example:

It gives me great pleasure to go and see all the beautiful kinds of fish in the modern aquarium, which shows you the wonderful world [that exists] at the bottom of the ocean. (First Certificate in English; B2; German)

B1 no plural the part of a road or area of land that is furthest from where you are
Dictionary examples:

They live at the bottom of our street.

The apple tree at the bottom of the garden has lots of fruit.

Learner example:

She could hear a sort of sad cat's voice from the bottom of the garden. (First Certificate in English; B2; Hungarian)

bottom (BODY PART)
B1 C the part of your body that you sit on
Dictionary example:

She slipped and fell on her bottom.

Learner example:

[There were two people holding] my arms and the third one on the ladder below me [hold]ing my bottom. (First Certificate in English; B2; Polish)

the bottom line
C2 the most important fact in a situation
Dictionary example:

The bottom line is that people's health is at risk if they smoke.

Learner example:

The bottom line is that the adults of today have to stop for a second and think about what they are doing. (Certificate of Proficiency in English; C2; Russian)

from top to bottom
C2 completely
Dictionary example:

I've searched the house from top to bottom and still can't find it.

Learner example:

Very often we can see someone in black, from top to bottom, or in white. (Certificate of Proficiency in English; C2; Chinese)

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