Error in emergency call, a firefighter sent the wrong way (7)
I believe the answer is:
fallacy
'error' is the definition.
(thesaurus)
'in emergency call a firefighter sent the wrong way' is the wordplay.
'in' indicates a hidden word.
'sent the wrong way' is a reversal indicator.
'ycallaf' can be found hidden inside 'emergency call a firefighter'.
'ycallaf' in reverse letter order is 'FALLACY'.
(Other definitions for fallacy that I've seen before include "The old lie" , "Incorrect notion based on false reasoning" , "'Misconception, false belief (7)'" , "Wrong but prevalent notion" , "Illogical argument" .)