Ambiguity caused by polysemy:
1.I saw a crane in the field.
"crane" is a polysemic word.It could mean either a bird or a machine that looks like a bird.
2.You should have seen the bull we got from the Pope.
The sentence is ambiguous,because the word bull may stand for several distinct things – either a male animal of different kinds,a swearword or an official order or statement from the Pope.
Ambiguity caused by homophones
1.I went to the bank yesterday.
The word "bank" could be the word that means the bank where I deposit money.It could also be the word that means the bank at a river or a lake.
2.The night (knight) is gone.
If the sentence is uttered rather than written,it may cause ambiguity because the hearer is not sure whether the speaker is talking about the night as opposed to the day,or someone who is good at fighting in the middle ages.