Idioms and set phrases are the hardest part of fluency and the part textbooks handle worst, which leaves an opening in the largest of this word’s markets. Phraseology is the study of set phrases, idioms and fixed expressions, and it’s also simply the way a particular field words things. Aviation phraseology is standardised and mandatory. Legal phraseology is a profession’s entire vocabulary. The linguistics reading suits a research resource, a corpus tool, a language learning product, or an academic project.