Overflow \O`ver*flow"\, v. t. [imp. & p. p. {Overflowed}; p. pr. & vb. n. {Overflowing}.] [AS. oferfl?wan. See {Over}, and {Flow}.] 1. To flow over; to cover woth, or as with, water or other fluid; to spread over; to inundate; to overwhelm. The northern nations overflowed all Christendom. --Spenser. 2. To flow over the brim of; to fill more than full.