From The Collaborative International Dictionary of English v.0.48:
De- \De-\
A prefix from Latin de down, from, away; as in debark,
decline, decease, deduct, decamp. In words from the French it
is equivalent to Latin dis- apart, away; or sometimes to de.
Cf. Dis-. It is negative and opposite in derange, deform,
destroy, etc. It is intensive in deprave, despoil, declare,
desolate, etc.
[1913 Webster]