Word: ambiguity

Context sentence: We have to recognize, then that there is ambiguity in the usage of the phrase'upper-middle class'.
Source:British Society Since 1945 Marwick

Definition:[uncountable and countable] the state of being unclear, confusing, or not certain, or things that produce this effect
eg:There was an element of ambiguity in the president's reply.

mnemonic: am-un big
so the word can be memorized as unbig-not big enougn so that cannot be seen clearly.