As an adjective, secret means kept hidden from knowledge or view. It usually describes actions, ideas, and things. Secretive, meaning having an inclination to secrecy, usually describes people, groups, or animals. For example, the phrase secretive project doesn’t make logical sense because a project can’t have an inclination to secrecy. To say that the project is secret would be more in keeping with the words’ conventional senses.
There is less distinction between the words’ corresponding adverbs, and secretly is very often used where secretively might make more sense.
Examples
Secret
This month marks the 40th anniversary of Henry Kissinger’s secret trip to Beijing. [CNN]
A secret memorandum of understanding between the UK and US on the treatment of prisoners captured in Iraq has been released for the first time. [Guardian]
The secret deployment reflects the concerns of military commanders that the withdrawal will be a blow to military progress in the country. [The Australian]
Secretive
U.S. President Barack Obama can command highly disciplined and secretive SEALs to hunt down Osama bin Laden and they’ll happily pull the trigger. [Calgary Herald]
The remains of a female northern goshawk, described as a large, powerful and secretive bird of prey, were found last week. [Washington Post]
He was the world’s richest and most secretive art collector before a dramatic fall from grace. [Independent]