V A R I A T I O N
/vɛːrɪˈeɪʃ(ə)n/
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a change or slight difference in condition, amount, or level, typically within certain limits.
synonyms: difference, dissimilarity, disparity, inequality, contrast, discrepancy, imbalance, differential, distinction -
ASTRONOMYa deviation of a celestial body from its mean orbit or motion.
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MATHEMATICSa change in the value of a function due to small changes in the values of its argument or arguments.the angular difference between true north and magnetic north at a particular place.
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BIOLOGYthe occurrence of an organism in more than one distinct colour or form.
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a different or distinct form or version of something.
synonyms: variant, alternative, alternative form, other form, adaptation, alteration, modification, revision
S I M I L A R I T Y
/sɪməˈlarəti/
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the state or fact of being similar.“the similarity of symptoms makes them hard to diagnose”
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a similar feature or aspect.“the similarities between people of different nationalities”
synonyms: resemblance, likeness, similitude, comparability, correspondence, comparison, parallel, equivalence. 
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try and extend your mind map to beyond just dictionary definitions. Its often in words associated with themes that you will find something that will give you ideas for starting points