Miss one stair, taking a tumble (8)
I believe the answer is:
senorita
'miss' is the definition.
(thesaurus)
'one stair taking a tumble' is the wordplay.
'taking a tumble' indicates an anagram.
'one'+'stair'='onestair'
'onestair' with letters rearranged gives 'SENORITA'.
(Other definitions for senorita that I've seen before include "Young lady of Spain" , "Notaries surrond Spanish girl" , "Abroad, miss" , "Treason I commit for young Spanish woman" , "miss from Valencia" .)