lock 2

lock

1

fastening

[countable] a thing that keeps a door, drawer etc fastened and is usually opened with a key or by moving a small metal bar:

I'm sorry, there isn't a lock on the bathroom door.

The key turned stiffly in the lock.

a bike lock

2

under lock and key

a) kept safely in a box, cupboard etc that is locked:

Dad keeps all his liquor under lock and key.

b) kept in a place such as a prison

3

lock, stock, and barrel

 including every part of something:

He moved the whole company, lock, stock, and barrel, to Mexico.

4

hair

a) [countable] a small number of hairs on your head that grow and hang together

lock of

He gently pushed a lock of hair from her eyes.

b) 

locks

[plural] literary someone's hair:

long flowing locks

5

on a river etc

[countable] a part of a canal or river that is closed off by gates so that the water level can be raised or lowered to move boats up or down a slope

6

in a fight

[countable] a hold which wrestlers use to prevent their opponent from moving:

a head lock

7

vehicle

[uncountable and countable] British English the degree to which a vehicle's steering wheel can be turned in order to turn the vehicle

8

rugby

[countable] a playing position in the game of rugby

9

a lock on something

American English complete control of something:

Pro football still has a lock on male viewers aged 18 to 34.

➔ air lock, combination lock

Definition from the Longman Dictionary of Contemporary English
Advanced Learner's Dictionary.