The plural is tota pro partibus, "wholes for parts".
In context of language, it means something is named after something of which it is only a part (or only a limited characteristic, not necessarily representative of the whole).
Notable examples include: The verb "to drink" is often used in this manner.
Depending on context it can stand for the generic, standard definition "to consume a liquid" (e.g. "I'm thirsty, is there anything to drink?")
or for the narrow, limited definition "to imbibe alcoholic beverages" (e.g. "He goes out to drink too often").