The term 'make invalid' can be defined as rendering something legally or officially ineffective. This can be done in a variety of ways, such as voiding, nullifying, annulling, or negating. The crossword solutions for this term are VOID (4 letters), NULLIFY (7 letters), ANNUL (5 letters), and NEGATE (6 letters). Voiding something means to declare it to be of no legal force or binding effect, while nullifying something means to make it legally invalid. Annulling something means to declare it to be legally invalid, while negating something means to make it ineffective or invalid.