blame - feel or declare that (someone or something) is responsible for a fault or wrong.
allegation - a claim or assertion that someone has done something illegal or wrong, typically one made without proof.
I don't understand what's the difference between these words. Aren't they synonyms?
Good question! They are not synonyms. I will try to explain the differences the best I can.
The first difference is that "Allegation" is a noun, and "Blame" is usually a verb. Blame can also a noun, but I think it is more common to use it as a verb. "Allegation" means "A claim that someone is guilty" (noun) and "Blame" means "to claim that someone is guilty" (verb). So the differences between your two definitions come down to the difference between claim as a verb and claim as a noun. Google gives the verb definition as
State or assert that something is the case, typically without providing evidence or proof.
and also gives the noun definition as:
An assertion of the truth of something, typically one that is disputed or in doubt.
So if I were to Claim (verb) that I just won the lottery, I stated or asserted that I won the lottery. I also made a claim (noun) that I just won the lottery. I made an assertion of the fact that I won the lottery.
Now as for "blame" as a noun, the differences are more obvious. "Blame" as a noun is synonymous with "guilt". If someone makes allegations that I am guilty, it is still a possibility that I am innocent. That only means that someone says that I am guilty. The same is true if someone blames (verb) me. However, if "The blame is on me" or "I take the blame" (both nouns) then it does not leave an option that I am innocent. It means that I am guilty.
They are quite different both syntactically and semantically.
Blame as a verb assigns responsibility to an agent for a deplorable fact or act. There are two constructions:
1) with the agent as direct object and the fact or act as object of the preposition for
He blames her for his brother's death.
He blames her for betraying his brother.
2) with the fact or act as direct object and the agent as object of the preposition on
He blames his brother's death on her.
He blames his brother's betrayal on her.
The noun blame usually designates responsibility for the act.
He assigns the blame for his brother's death to her.
She is at blame for his brother's death.
The verb allege merely asserts a fact. It is frequently used in contexts where the fact is some criminal or improper action; but it is not confined to that context. In fact, it is most often encountered in news stories where it serves as a 'hedge' to emphasize the reporter's neutrality with respect to the assertion. Allege usually takes a that clause as its object, but it may also take a noun phrase:
The police complaint alleges that he robbed the convenience store.
Sen. Hill alleges that the Commerce Department is too friendly with industry.
Prof. Sartorius alleges that the name 'Moses' should be understood as Egyptian msy, 'he is born'.
Prof. Sartorius an Egyptian origin for the name Moses.
The noun allegation designates either an act of alleging or the fact alleged. It may take a that clause or of + noun phrase as its complement.
The police have made serious allegations against him.
Sen. Hill has made the news again, with allegations of Commerce Department improprieties.
Prof. Sartorius' allegation that the name 'Moses' should be understood as Egyptian msy, 'he is born' is not widely endorsed.
