arbitrary

definition: 
Based on random choice or personal whim, rather than any reason or system:
sentence: 
This numbering system is an arbitrary designation based on small amino acid sequence differences
difficulty: 
very easy
toefl frequency: 
3
toefl classification: 
adverb: 
arbitrarily
adjective: 
adverb sentence: 
The professor arbitrarily decided to give the class a test.
adjective sentence: 
verb: 
verb sentence: