Rita's out of step (5)
I believe the answer is:
stair
'step' is the definition.
(a single step in a staircase)
'rita's out' is the wordplay.
'out' is an anagram indicator (out can mean wrong or inaccurate).
'ritas' anagrammed gives 'STAIR'.
'of' is the link.
(Other definitions for stair that I've seen before include "means to go down" , "Step as part of flight" , "that's between levels" , "A step on the way up or down" , "Step in house" .)