Question: Here is one sentence: Air pollution.
Here is another sentence: Her hand stopped in mid air.
Does the air mean the same thing in the two sentences?

Answer: different meanings

Question: Here is one sentence: The judge leniently granted a sentence with no hard time.
Here is another sentence: He is not living at home because he is doing time.
Does the time mean the same thing in the two sentences?

Answer: the same meaning

Question: Here is one sentence: Change per unit volume.
Here is another sentence: He was a member of a special police unit.
Does the unit mean the same thing in the two sentences?

Answer: different meanings

Question: Here is one sentence: Pay a visit.
Here is another sentence: It pays to go through the trouble.
Does the pay mean the same thing in the two sentences?

Answer:
different meanings