If you are referring to priming studies, primes and target words can be 1) semantically related or unrelated, or less commonly 2) morphologically related or unrelated. 

Thank you so much

Hi,

Words can be related or not in terms of semantics,i.e. words are related if they are meaningful.

Related words are words that are able to make greater sense and meaning when they are put together in the construction of sentences. Their agreeability fosters a richer and greater understanding.

Unrelated words are words that when put together in a particular context may blur or thwart the meaning and understanding of a particular sentence or composition, especially for lower grade learners.

However, some writers cleverly portray unrelated words in writings such as poems, novels and so forth to throw more light on an issue or emphasize a trait of a character just to garnish the flavor of the writing.This must be used in moderation since excessive use may confuse readers especially those at the lower levels of education. For a proper level of difficulty, the writer must carefully use both related and unrelated words. This decision that determines the parameters for measuring readability must be made based on the age range of readers and learners.

Dickson Adom

Wonderful answer dear Dickson Adom.  I agree with you totally. 

Liqaa 

Thank you dear Prof. Liqaa. 

Thoughtful question and very nice answer from Dr Adom.