The IC Rule (Major)

This Rule applies to those words in English with two or more syllables that end with the letters

....ic

To translate them into Spanish, we will substitute the ending with

...ico

As an example, the English word rustic is the Spanish word rústico.
A reminder: this ending is pronounced EE-KO
Rústico, then, is pronounced ROOS-TEE-KO
This Rule applies to many useful words in Academia (Chemistry, Geography, Physics, Medicine, etc.) as well as common-usage words.
These are irregular words and therefore receive written accents as shown. The stress, of course is on the syllable where the written accent is located. The accent is always written above the vowel in that syllable (See ACCENTS in Chapter One), so here are some Examples

The IC Rule

English Spanish Helpful Reminders
...ic ...ico
Academic Académico
Acidic Acídico
Allergic Alérgico only 1 L
Aquatic Acuático
Arctic Ártico [1] note at the end of the chapter
Baltic Báltico
Barometric Barométrico
Caloric Calórico
Caustic Caústico
Clinic Clínica feminine gender
Critic Crítico
Eccentric Excéntrico XC for CC
Empiric Empírico
Fanatic Fanático
Fantastic Fantástico
Galactic Galáctico
Gastric Gástrico
Geographic Geográfico quirks #5 & #12
Harmonic Armónico no H
Hemostatic Hemostático quirk #1
Intrinsic Intrínseco E for I
Juridic Jurídico
Kinetic Kinético
Linguistic Lingüístico Ü for U
Logic Lógica [2] feminine gender
Magic Mágico
Magnetic Magnético
Microscopic Microscópico
Mimic Mímico
Nordic Nórdico
Ophthalmic Oftálmico quirk #5, no TH
Organic Orgánico
Orthopedic Ortopédico no TH
Panic Pánico
Plastic Plástico
Problematic Problemático
Quadratic Cuadrático C for Q
Quartic Cuártico C for Q
Republic República [2]
Rhetoric Retórico no RH
Semantic Semántico
Septic Séptico
Simplistic Simplístico
Symphonic Sinfónico IN for YM, quirk #5
Telegraphic Telegráfico
Tonic Tónico
Toxic Tóxico quirk #9
Umbilic Umbílico
Uric Úrico
Vitalic Vitálico
Vocalic Vocálico
Volcanic Volcánico
Xenophobic Xenofóbico X pron. like S, quirk #9

An exception to this Rule, is:

English Spanish Helpful Reminders
Mastic Mastique

This rule also covers many scientific words:

Chemical Terms
English Spanish Helpful Reminders
Aceric Acérico
Acetic Acético
Citric Cítrico
Hydrochloric Clorhídrico [3] I for Y
Lactic Láctico
Sulphuric Sulfúrico quirk #5
Violuric Violúrico
Medical Terms:
English Spanish Helpful Reminders
Arrhythmic Arrítmico I for Y, no TH
Hemostatic Hemostático quirk #1
Hepatic Hepático quirk #1
Palludic Paludic only 1 L
Spasmodic Espasmódico quirk #6
Spastic Espástico quirk #6
Engineering Terms:
English Spanish Helpful Reminders
Electronic Electrónico
Galvanic Galvánico
Metric Métrico
Mathematical Terms:
English Spanish Helpful Reminders
Algebraic Algebraico
Quadratic Cuadrático C for Q
Cubic Cúbico
Mathematic Matemático no TH

and hundreds more that you shouldn't have any trouble thinking of!

[1] Interesting word, Arctic; Although in English it is still correct to spell the word with two "c's" (which at one time was also the Spanish spelling: Ártico) the Spanish version has dropped one of the "c's". Strangely, though, the English spelling for "Artichoke" -that delightful cold-climate thistle flower which we eat- is no longer spelled "Arctichoke" (although, until relatively recently, it was). Because most people pronounce the word Arctic as "Artic", it is probably just a matter of time before the spelling is changed. Just a bit of trivia...

[2] You may have noüced that Clinic, Logic, and Republic in Spanish, are Lógica, Clínica and República ! These are feminine-gender words! We will get into that a bit later on in the book...!

[3] As we tearned in Chapter One, Spanish is a mirror image of English in that the adjective (modifier) comes after the object. In these cases, it is the hydrogen that modifies the fluorine and chlorine, hence the "switch".