The phrase "demand back" refers to the act of requesting the return of something that was previously given or lent to someone. There are several synonyms that can be used to convey a similar meaning, such as "reclaim," "retrieve," "recover," "repossess," and "retake." Each of these terms implies a sense of ownership and the desire to regain possession of something that belongs to the speaker. Other synonyms might include "take back," "withdraw," or "revoke," all of which suggest a reversal of a previous action or decision. Ultimately, the choice of synonym will depend on the particular context and tone of the sentence.