The word "挥之不去" is formed by combining the verb "挥" (meaning to wave or dismiss) with the object pronoun "之" (meaning it), followed by the negation "不" and the verb "去" (meaning to go away), resulting in a grammatical structure where "挥之" acts as the action-object pair and "不去" serves as a negated result complement, literally expressing "wave it but it does not go away" to indicate something persistent.