a group of words with a meaning that is not obvious through knowledge of the individual words but must be learnt as a whole, e.g. 'give up, in order to, be all ears'

manner of speaking, turn of phrase

a style of a language full of technical or special words

specialized language; dialect

any of several languages having elements of a local language and English, French or Dutch

casual dialect

words, phrases, meanings etc sometimes used in very informal conversation but not suitable for writing or for more formal occasions

casual dialect