Ўзбекистон республикаси олий ва ўрта махсус таълим вазирлиги ўзбекистон давлат жаҳон тиллари университети инглиз тили назарий аспектлари №1

Phraseological fusions are completely non-motivated phraseological units, such as red tape – ‘bureaucratic methods’; heavy father – ‘serious or solemn part in a theatrical play’; kick the bucket – ‘die’; and the like. The meaning of the components has no connections whatsoever, at least synchronically, with the meaning of the whole group.
Idiom is a set expression which is fully non-motivated as its meaning can not be deduced from the meanings of the words which are its structural components.
Idiomaticity, or lack of motivation, is complete or partial inconsistence with the form or structure of a lexical unit and its meaning.