niggling vs proficient

niggling

noun

  • A small irritating sensation. 

adj

  • Petty 

  • Irritating. 

proficient

noun

  • An expert. 

adj

  • Good at something; skilled; fluent; practiced, especially in relation to a task or skill. 

How often have the words niggling and proficient occurred in a corpus of books? (source: Google Ngram Viewer )