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The word you're looking for is "mat." By changing the letter "h" in "hat" to "m," you get "mat," which can be associated with being open to change, as in a welcome mat or a mat that signifies an entrance.
cart
Try the word place or plane.
clat
bite bile file fill foll fool food
Seat
The antistatic mat is that one which is one which is in motion. To make the antistatic mat one needs to incorporate a few electronic device like the thermostats.
how do you change disaster to mean one letter at a time
The word "pen" would change to "men" if one letter is altered.
rearrange N and E and change the first letter.
When speaking of a "Coir Door mat", one refers to a small mat placed at the entrance. This kind of mat does a good job of scrubbing dirt off the shoes and does not trap water under it.
A small bed is often referred to as a "cot." If you change one letter in "cot," you can get "dot."