1 to use

2 to employ

3 to apply

4 to make use of

1 weaponry

2 weapons

3 arms

1 to use

2 to employ

3 to have to

4 to eat or drink

5 expense or outlay

6 usefulness

7 hence

8 therefore

1 user

2 consumer

3 subscriber

4 customer

1 to go through

2 to know well

3 (suffix) expert

4 to connect

5 to communicate

6 open

7 to clear

8 classifier for letters, telegrams, phone calls etc

1 to do two things at once (idiom)

2 to multitask

3 to divide one's attention

1 lit. doesn't (even) enter a single aperture (of one's head)

2 I don't understand a word (idiom)

3 it's all Greek to me

1 grasp this fundamental point and all the rest will follow (idiom)

1 spare the rod and spoil the child (idiom)

1 to act in collusion (idiom)