Flat on the floor, one may welcome you (3)
I believe the answer is:
mat
'flat' is the definition.
(I know that flat can be written as mat)
'on the floor one may welcome you' is the wordplay.
I cannot quite understand how this works, but
'on' could be 'at' (I've seen this in other clues) and 'at' is located in the answer.
A single letter 'm' remains which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for mat that I've seen before include "Shoe-cleaner" , "Paint with a dull surface" , "Unglossy floor pad" , "Rough piece of floor-covering" , "Small carpet" .)