| heliac | (adjective) pertaining to or near the sun; especially the first rising of a star after and last setting before its invisibility owing to its conjunction with the sun | Synonyms: heliacal |
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| heliacal | (adjective) pertaining to or near the sun; especially the first rising of a star after and last setting before its invisibility owing to its conjunction with the sun | Synonyms: heliac |
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| helianthemum | (noun) any plant of the genus Helianthemum; vigorous plants of stony alpine meadows and dry scrub regions | Synonyms: sun rose, sunrose |
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| helianthus | (noun) any plant of the genus Helianthus having large flower heads with dark disk florets and showy yellow rays | Synonyms: sunflower |
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| helical | (adjective) in the shape of a coil | Synonyms: coiling, spiral, spiraling, spiralling, turbinate, volute, voluted, whorled |
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| helicon | (noun) a tuba that coils over the shoulder of the musician | Synonyms: bombardon |
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| helicopter | (noun) an aircraft without wings that obtains its lift from the rotation of overhead blades | Synonyms: chopper, eggbeater, whirlybird |
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| heliocentric | (adjective) having the sun as the center | - |
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| heliogram | (noun) a message transmitted by means of the sun's rays | - |
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| heliograph | (noun) an apparatus for sending telegraphic messages by using a mirror to turn the sun's rays off and on | - |
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| (verb) signal by means of a mirror and the using the sun's rays | - |
| heliogravure | (noun) an intaglio print produced by gravure | Synonyms: gravure, photogravure |
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| heliolatry | (noun) the worship of the sun | Synonyms: sun-worship |
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| heliometer | (noun) an instrument used to measure the angular separation of two stars that are too far apart to be included in the field of view of an ordinary telescope | - |
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| heliopause | (noun) the boundary marking the edge of the sun's influence; the boundary (roughly 100 AU from the sun) between the interplanetary medium and the interstellar medium; where the solar wind from the sun and the radiation from other stars meet | - |
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| heliophila | (noun) any of various South African herbs and subshrubs cultivated for long showy racemes of bright blue flowers with white eyes | - |
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| heliopsis | (noun) any North American shrubby perennial herb of the genus Heliopsis having large yellow daisylike flowers | Synonyms: oxeye |
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| heliosphere | (noun) the region inside the heliopause containing the sun and solar system | - |
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| heliotherapy | (noun) therapeutic exposure to sunlight | Synonyms: insolation |
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| heliotrope | (noun) green chalcedony with red spots that resemble blood | Synonyms: bloodstone |
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| heliotropism | (noun) an orienting response to the sun | - |
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| heliotype | (noun) duplicator consisting of a gelatin plate from which ink can be taken to make a copy | Synonyms: hectograph |
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| heliozoan | (noun) protozoa with spherical bodies and stiff radiating pseudopods | - |
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| heliport | (noun) an airport for helicopters | - |
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| helium | (noun) a very light colorless element that is one of the six inert gasses; the most difficult gas to liquefy; occurs in economically extractable amounts in certain natural gases (as those found in Texas and Kansas) | Synonyms: atomic number 2, He |
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| helix | (noun) a structure consisting of something wound in a continuous series of loops | Synonyms: coil, spiral, volute, whorl |
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| (noun) a curve that lies on the surface of a cylinder or cone and cuts the element at a constant angle | Synonyms: spiral |