Taciturn (5-6)
'taciturn' is the definition.
(similar in meaning)
This is all the clue.
(Other definitions for reticent that I've seen before include "Uncommunicative" , "Not revealing one's thoughts readily" , "Reserved, shy" , "Reserved, retiring" , "Disinclined to speak" .)
'taciturn' is the definition.
(thesaurus)
This is all the clue.
(Other definitions for tight-lipped that I've seen before include "Uncommunicative" , "Determinedly reticent" , "Taciturn" .)