Tier; use oars (3)
I believe the answer is:
row
This clue is a double definition.
'tier' is the first definition.
(eg a row of seats at a theatre)
'use oars' is the second definition.
(I've seen this in another clue)
(Other definitions for row that I've seen before include "Use an oar" , "Fight in a queue?" , "Propel with oars" , "Propel boat with manual aids" , "Quarrel; use oars" .)