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Pronunciation: dai-æg-nah-stik Hear it!

Part of Speech: Adjective, Noun

Meaning: 1. (Adjective) Distinctive, characteristic, indicative, as a diagnostic feature of tigers is their stripes. 2. (Adjective) Related to diagnosis, as a diagnostic test or laboratory. 3. (Noun) A distinctive characteristic or characteristic symptom, as fever is one diagnostic of influenza.

Notes: Today's word is used so widely in science, particularly medicine, that it has spilled over into the general language. The noun underlying this word is diagnosis and the verb lying beneath that noun is diagnose. As everywhere in Greek, the origin of today's word, T replaces S in all words derived from words ending on S, e.g. neurosis : neurotic, narcosis : narcotic, symbiosis: symbiotic.

In Play: This word is used mostly in connection with an illness or debility, and as an adjective: "The city doctor didn't know what diagnostic tests to run for trichinosis." But it is also used as a noun: "The inability to walk in a straight line is one diagnostic of inebriation." However, this word works as well outside the field of medicine: "Blushing at the mention of one name is a sure diagnostic of love."

Word History: Today's Good Word was taken from French diagnostique from Greek (via Latin) diagnostikos "able to distinguish (diseases)". This adjective is based on diagnostos, the verbal adjective from diagignoskein "to distinguish, discern". This word is made up of dia- "apart" + gignoskein "to learn". Dia- is related to Latin dis- as copied by English in dismember, discharge, and so on. The root of the verb gignoskein is gno- "know", from the same source as English know and Latin gnomon "pointer on a sundial". (If suggesting Good Words is a diagnostic of a true logophile, today's recommender, Jeremy Busch, our on-site editor and Grand Panjandrum in the Alpha Agora, certainly is one.)

Dr. Goodword,

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