dad
Dud
dew
A seven letter word that starts with D and ends with T: decrypt
discard
watched.
unoccupied
Lighthearted is a 12 letter word. Lithographed is another 12 letter word that starts with L and ends with D.
Domain is one of the words that starts with the letter D and ends with the letter N.
The five letter word that is the opposite of behind and begins with an 'a' and ends with a 'd' is AHEAD.
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dogging
One word that fits your criteria is "distant." It starts with the letter 'd,' ends with 't,' and contains seven letters.