kalliste

I thought I had made my point - that a phrasal lexeme can be a few words - take "cats and dogs" - whereas the expression "raining cats and dogs" - meaning that the weather is atrocious and doesn't mean the same as "fighting cat and dog" meaning a really ill-natured fight between two diametrically opposed sides. A phrasal lexeme always has the potential to become an part of an idiom - a unique meaning - as opposed to an idiom which has a specific, unique meaning all of it's own. Idioms can contains phrasal lexemes, but a phrasal lexeme wouldn't contain an idiom. On the other hand, I suspect you are right, it is just about "how long the phrase" and "how specific" the idiom.

An idiom or idiomatic phrase is usually a longer string of words that has a specific meaning that no amount of understanding the individual word meanings (lexemes) will explain. If the word order is changed the meaning is lost. Eg "Red light district" has a specific meaning that has nothing to do with red or light or red light although it is still a type of district. Similary for "raining cats and dogs". A phrasal lexeme is a short string, usually only two words where adding the extra word tends to qualify the meaning of both, although I suspect eventually the phrasal lexeme enters the language as an idiom as it gets longer, because it acquire "universal" acceptance as a specific meaning, and no longer has the flexibility to be used in several different situations. Eg wind up does not mean the same as wind or up, let alone up wind - but it's short enough to allow itself to be adapted into several longer phrases - wind up toy, wind up merchant, up wind, stand up wind. which in turn become idioms as the phrase crystallises into a single recognisable "lexeme" itself.