Engineers carpet to have clean covering, but too early (9)
I believe the answer is:
premature
'too early' is the definition.
(thesaurus)
'engineers carpet to have clean covering' is the wordplay.
'engineers' becomes 're' (Royal Engineers).
'carpet' becomes 'mat' (I've seen this before).
'to have clean' becomes 'pure' (I can't explain this - if you can you should believe this answer much more).
'covering' is an insertion indicator.
're'+'mat'='remat'
'remat' going inside 'pure' is 'PREMATURE'.
'but' acts as a link.
Can you help me to learn more?
(Other definitions for premature that I've seen before include "Before the normal time" , "Born before full term" , "not fully developed" , "Untimely" , "Too soon or too hasty" .)