It is the hypothetical source of/evidence for its existence is provided by: Sanskrit svanati "it sounds," svanah "sound, tone;" Latin sonus "sound, a noise," sonare "to sound;" Old Irish senim "the playing of an instrument;" Old English geswin "music, song," swinsian "to sing;" Old Norse svanr, Old English swan "swan," properly "the sounding bird."
noun word-forming element, "that which is written or marked," from Greek gramma "that which is drawn; a picture, a drawing; that which is written, a character, an alphabet letter, written letter, piece of writing;" in plural, "letters," also "papers, documents of any kind," also "learning," from stem of graphein "to draw or write" (see -graphy). Some words with it are from Greek compounds, others are modern formations. Alternative -gramme is a French form.
From telegram (1850s) the element was abstracted by 1959 in candygram, a proprietary name in U.S., and thereafter put to wide use as a second element in forming new commercial words, such as Gorillagram (1979), stripagram (1981), and, ultimately, Instagram (2010). The construction violates Greek grammar, as an adverb could not properly form part of a compound noun. An earlier instance was the World War II armed services slang latrinogram "latrine rumor, barracks gossip" (1944).
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Definitions of sonogram from WordNet
an image of a structure that is produced by ultrasonography (reflections of high-frequency sound waves); used to observe fetal growth or to study bodily organs;