Infuse vs. Suffuse

What’s the difference between infuse and suffuse? To infuse something is to literally or figuratively fill it; the senses include “animate,” “inject,” “inspire,” “introduce,” “permeate,” and “steep.” One that or who infuses is an infuser, the act of infusing is called infusion. Suffusion is a closely related concept, but suffuse means, in addition to “fill,” to “spread over or through,” as if with light or liquid; synonyms include flush.

These terms and their several cousins all have in common a root based on the Latin term fundere, meaning “pour,” and are related to the verb found in the sense of melting and pouring into a mold, as is done at a foundry. (The other senses of found, the past-tense form of find and the word meaning “establish,” have separate origins.)

Etymologically related words include fuse in the sense of “blend or join” and its noun form fusion. (The noun fuse, referring to an electrical device or a cable or cord used in lighting an explosive—in the latter sense, also spelled fuze—is unrelated.) Then there’s confuse, meaning “make difficult to understand,” “cause someone difficulty in understanding,” or “mistake someone or something for another”; the synonym confound, which can also mean “prove wrong” as well as “increase confusion,” has the same origin.

Diffuse means “spread out”; the adjectival form means “not concentrated.” The quality of being diffuse is diffuseness, and the noun form for the act of spreading out is diffusion. (Diffuse is not to be confused with defuse; that word is an antonym of the unrelated sense of fuse.) Effuse is a synonym for diffuse in the sense of being spread out amorphously; the verb form, used more often than the adjectival form, means “pour out” or “display much or excessive enthusiasm.” (The adjectival form for the latter sense is effusive.)

Perfuse is a rare synonym for diffuse or suffuse with the additional sense of forcing the flow of a liquid through something (it has no adjectival form), and transfuse, meaning “permeate” or “transmit,” also has a sense of “transfer”; the common noun form associated with this meaning is transfusion. (Something that can be transfused is transfusible; that word is sometimes spelled with an a instead of an i.)

The noun and verb forms of refuse are unrelated; its Latin progenitor, refusare, probably originated as a mash-up of refutare and recusare, the Latin words from which refute and recuse are derived.