Which word best matches the definition "to make free"?

The term "liberate" directly aligns with the definition "to make free," as it specifically refers to the act of setting someone free from restrictions, control, or oppression. When one liberates another, they are allowing that individual to experience freedom or autonomy from bondage or limitations, effectively making them free.

The context of the other options illustrates their specific meanings: "emancipate" also means to free, particularly from legal, social, or political restrictions, but it may carry a more specific historical connotation, particularly regarding the abolition of slavery. "Constrain" signifies the opposite of making free, implying restriction or limitation. "Annex" refers to the act of adding or attaching territory, which does not relate to the concept of freedom at all. Thus, "liberate" is the word that best encapsulates the essence of making free in a broad and general sense.