De is a prefix that can be used with legacy. It spells the word delegacy. It means the act of delegating.
It would be either a prefix or a suffix. Prefix means the letters before, and suffix means the letters after the word.
overjoyed
Colossal.
pensive
A word that begins with the prefix "pac" is "pacific," which means peaceful or calm.
Nonagon is a word that begins with the prefix "non" and means a polygon with nine sides.
The prefix for inadequate is in-. The prefix in- means not.
recall
A duet.
Not a word, but a prefix "milli".
The prefix for the word polymyositis is "poly-," which means many or much.
The prefix in non-. This prefix means not.
I am not sure what your question is really asking but it sounds like the word anti may be what you are looking for. It is a prefix that when used before a word makes its meaning the Social, becomes anti social. a word with the direct opposite meaning AntiChrist AntiVirus etc. there are tonnes of examples
The prefix in the word "atheist" is "a-", which means "without" or "not."
The prefix in the word "confide" is "con-," which means "with" or "together."
The prefix in the word mannerly is man-. This prefix means hand.