The phrase "didst top head" is an archaic way of saying "you cut off someone's head." Synonyms for this phrase can be more modern and include terms like "beheading," "decapitation," or "removing the head." Other synonyms for this phrase might include "severing the head," "cutting off the head," or "chopping off the head." These terms are more commonly used in today's language but still convey the same meaning as "didst top head." Remember, using accurate and appropriate language is crucial when describing actions that involve violence or harm.