Facts in emergency (3)
I believe the answer is:
gen
'facts' is the definition.
(thesaurus)
'in emergency' is the wordplay.
'in' indicates the answer is hidden within the clue.
'GEN' is hidden within 'emergency'.
(Other definitions for gen that I've seen before include "Information yielded" , "Lowdown (sl.)" , "Info" , "Knowledge" , "opening book, in short" .)