What’s the difference between testimony and testimonial? The former word refers to formal presentation of facts, while the latter, while denoting the same meaning, has a more qualitative connotation in which opinion (and perhaps deception) is expressed as well.
Testimony means “the statement of a witness” and is used generally used only in a legal sense; originally, it also referred to evidence, but that sense is obsolete. Testimonial, as an adjective, means “of or pertaining to testimony,” but as a noun it means “a statement of one’s character or qualifications.”
This sense has been extended to refer to a common type of advertising in which a person testifies to the efficacy or quality of a product, as well as to a gift symbolizing appreciation. And just as testimony may be faulty or may involve perjury, testimonials are not necessarily reliable or deserved.
Testify, meanwhile, is a verb meaning “to bear witness.” A related word is testament, from the Latin word testamentum, meaning “a will” or “publication of a will”; it derives ultimately from testis, meaning “witness.”
Other words with the syllable -test include the verbs attest (“affirm” or “prove”), contest (“dispute” or “oppose,” originally in the sense of witnessing against someone, but now also meaning “compete”), detest (with the original sense of “denounce” but now generally meaning “abhor, dislike intensely”), and protest (originally, “declare or state formally or solemnly” but now meaning “complain” or “speak out against”); noun forms of contest and protest and nouns extending from attest and detest (attestation and detestation); and adjectival forms such as detestable.
The syllable -test in these words is related to Indo-European root word for “three”; the connection is that a third person, ostensibly neutral, is the ideal witness for providing testimony. Also, curiously enough, the word test, as a synonym for exam or trial, probably has no connection to the Latin syllable; it comes from the unrelated Latin word testum, meaning “earthen pot,” the earliest type of vessel used for assaying precious minerals. (This term is related to texere, meaning “to weave,” from which we get the word textile.)
Testicle (plural testicles, medical terms testis and testes), meanwhile, is associated with the sense of witnessing, perhaps in that the male reproductive organ bears witness to virility; one scholar, however, does make a connection between testis, the Latin origin of testicle, and testum, the Latin word for a pot.