Vague teatime, dinner breaks (13)
I believe the answer is:
indeterminate
'vague' is the definition.
(I've seen this before)
'teatime dinner breaks' is the wordplay.
'breaks' indicates an anagram.
'teatime'+'dinner'='teatimedinner'
'teatimedinner' anagrammed gives 'INDETERMINATE'.
(Other definitions for indeterminate that I've seen before include "Not exactly defined" , "Unspecified" , "uncertain result?" , "Not precisely fixed" , "not exactly fixed" .)