Source : Webster's Revised Unabridged Dictionary (1913)

Isologous \I*sol"o*gous\, a. [Iso- + Gr. lo`gos proportion.]
   (Chem.)
   Having similar proportions, similar relations, or similar
   differences of composition; -- said specifically of groups or
   series which differ by a constant difference; as, ethane,
   ethylene, and acetylene, or their analogous compounds, form
   an isologous series.