Step sibling's first tear, we hear (5)
I believe the answer is:
stair
'step' is the definition.
(a single step in a staircase)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for stair that I've seen before include "section of flight" , "One step of a flight" , "One of a 15" , "Rising step" , "single step in a series" .)