Secret signal (8)
I believe the answer is:
intimate
This might be a double definition.
'secret' is the first definition.
(thesaurus)
'signal' is the second definition.
Both the definition and answer are adjectives. Perhaps there's a link between them I don't understand?
Can you help me to learn more?
(Other definitions for intimate that I've seen before include "Give hint to close friend?" , "Personal - hint - friend" , "Thick" , "Infer; personal" , "Sharing a close and affectionate friendship" .)