• Webster's Revised Unabridged Dictionary
    • a Synthermal Having the same degree of heat.
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Century Dictionary and Cyclopedia
    • synthermal Having the same temperature.
    • n synthermal A line connecting places having the same temperature at the same moment of time; an isotherm based upon simultaneous observations, as distinguished from one based on synchronous local time observations.
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Chambers's Twentieth Century Dictionary
    • adj Synthermal sin-thėrm′al having the same degree of heat.
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Webster's Revised Unabridged Dictionary
Pref. syn-, + thermal,
Chambers's Twentieth Century Dictionary
Gr. syn, together, thermē, heat.