Flight unit (5)
'flight unit' is the definition.
(I've seen this before)
'unit' is the wordplay.
I cannot quite understand how this works, but
'unit' could be 'air' (air unit is a kind of unit) and 'air' is present in the answer.
The remaining letters 'st' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for stair that I've seen before include "A step on the way up or down" , "one's seen in flight" , "One step in a series" , "Set of steps" , "means to go down" .)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">flight unit</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for step that I've seen before include "Action of the leg" , "Foot movement" , "Second half of quick 20?" , "Tramp" , "Pace - part of a procedure" .)