


actin (s), actine (pl) (nouns)
2. A protein forming the thin filaments in muscle fibers that are pulled on by myosin cross-bridges to cause a muscle contraction.

Some bacteria form actin tails to use for motility.



actinal (adjective)
The region from which the rays or tentacles grow on a radiate animal.
actinian (adjective)
A reference to a sea anemone or a related ray-type animal.
actinic (adjective)
1. A reference to radiation; such as, sunlight or x-rays: "Sunburn is an actinic burn while actinic keratosis is a skin lesion that is caused by chronic sun exposure."
2. Possessing photochemical properties.
3. Pertaining to or designating radiant energy: "An actinic ray exists in the visible and ultraviolet spectrum which produces marked chemical changes."
actinic burn (s), actinic burns (pl) (nouns)
A burn, or burns, caused by exposure to sunlight or another source of ultraviolet radiation.
actinic carcinoma (s); actinic carcinomas, actinic carcinomata (pl) (nouns)
A basal cell or squamous cell cacinoma of the face and other exposed surfaces of the body, seen in people who spend prolonged periods of time in direct sunlight.
actinic conjunctivitis (s) (noun); actinic conjunctivitides, actinic conjunctivitises (pl)
An inflammation of the conjunctiva (transparent membrane covering the eyeball): "Actinic conjunctivitis can be caused by exposure to the ultraviolet radiation of sunlight or other sources; such as, exposure to acetylene torches, therapeutic lamps (sun lamps), and klieg lights (powerful carbon-arc lamps producing intense light and used especially in making movies)."

"Actinic is a term for ultraviolet (UV) rays from sunlight and UV lamps."

actinic dermatitis (s); actinic dermatitises, actinic dermatitides (pl) (nouns)
Inflammation of the conjunctiva and cornea with pain, photophobia, lacrimation, and smarting of the lids caused by repeated flashes of bright light or ultraviolet radiation.
actinic keratoses, solar keratoses, senile keratosis, senile wart
1. A focal, scaly excrescence on the scalp, face, neck, or other exposed surface of skin resulting, at least partially, from long exposure to the ultraviolet rays of the sun: "These actinic keratoses or solar keratoses are growths that are usually pink or red and appear as flaky, rough scaly patches or areas of skin and they may also be light gray or brown and feel hard, rough, or gritty.
2. Actinic keratoses (solar keratoses) are precancerous growths caused by long-term sun exposure.



Actinic keratoses usually can be removed by freezing with liquid nitrogen (cryotherapy); however, if a person has too many growths, a liquid or cream containing fluorouracil may be applied.


A relatively new drug, imiquimod, is useful in treating actinic keratoses because it helps the immune system to recognize and to destroy cancerous skin growths.

Another treatment includes cutting the keratoses away, by burning them with photodynamic therapy; that is, injecting into the bloodstream a chemical that collects in actinic keratoses and makes them more sensitive to destruction by a specialized form of light.

—Partially compiled from excerpts found in
Webster's New World Medical Dictionary; Wiley Publishing, Inc.;
Hoboken, New Jersey; 2008; page 6.
actinide, actinide series

The related chemical elements include: actinium, thorium, palladium, uranium, neptunium, plutonium, americium, curium, berkelium, californium, einsteinium, fermium, mendelevium, nobelium, and lawrencium.

1. Having or displaying a ray-like or radial form; rayed.
2. Exhibiting radiate form or structure; such as, the ray fungus or the sea anemone.
1. The ability of sunlight or similar forms of radiation to produce chemical changes.
2. The intrinsic property in radiation that produces photochemical activity.
3. The production of chemical change by actinic radiation.
A radioactive element found in uranium ores, used in equilibrium with its decay products as a source of alpha rays; such as, pitchblende (a mineral consisting of uranium oxide and trace amounts of radium and thorium and polonium and lead and helium; uraninite in massive form is called pitchblende which is the chief uranium ore).


Its longest lived isotope is Ac 227 with a half-life of 21.6 years. Atomic number 89; melting point 1,050°C; boiling point (estimated) 3,200°C; specific gravity (calculated) 10.07; valence 3.

1. An infectious disease of cattle, domestic animals, and occasionally humans, resembling actinomycosis and caused by the bacterium Actinobacillus lignieresii.

Actinobacillus lignieresii infects cattle and sheep while actinobacillosis Equuli infects horses and pigs.
