What's That Flat?

Transpogram

A word or phrase becomes another when divided into two parts, which are interchanged. Examples: rock-hard, hard rock (referring to the kind of music) ; or fast break, breakfast . Answers must be dictionary entries (or well known) but the parts need not be: for example, alloy, loyal .

A transpogram is most interesting if the parts have substantially different meanings. Houseguest and guest house, for example, are a dull base. Since interesting bases are hard to come by, the transpogram has always been an uncommon type.

In the phonetic transpogram, the two parts that switch remain true to sound but not to spelling. Examples: welfare, farewell; or Dear John (a kind of letter), John Deere (a brand name); or zero, rosy.