IPA: /ˌoʊvərɪˈmædʒɪnətɪv/
KK: /oʊvərɪˈmædʒɪnətɪv/
Having an imagination that is too strong or excessive, often leading to unrealistic ideas or thoughts.
Her overimaginative stories often took her friends on wild adventures that were hard to believe.
Overimaginative → It is formed from "over-" (meaning excessively) and "imaginative" (from Latin "imaginari", meaning to form a mental image). The word "overimaginative" describes someone who excessively forms mental images or ideas, often to the point of being unrealistic.
Think of someone who is 'excessively' ('over-') creating 'mental images' ('imaginative') — that's why overimaginative means having an excess of imagination.