Small dachshunds say, going up stairs (5)
I believe the answer is:
steps
'stairs' is the definition.
('step' can be a synonym of 'stair')
'small dachshunds say going up' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'dachshunds say' becomes 'pets' (dachshund is a breed of dog).
'going up' says the letters should be written in reverse.
's'+'pets'='spets'
'spets' in reverse letter order is 'STEPS'.
(Other definitions for steps that I've seen before include "Small ladder" , "stair" , "Buchan's 1915 novel has 39 of them" , "Sequence of foot movements in a dance" , "Measures taken" .)