I'm a ten-letter word, but when I am heard,
I have only four, not one letter more.

My first two sounds are neat; a kind of sheet,
That starts with spread, not the kind on a bed.

Of my sounds, the third is what will be heard,
alphabetically, in the middle of modus operandi.

If you want to hear more, then like the shore,
I end at the sea, that's a hint, you see.

What word am I?