Supply that supports a US city (3,2)
I believe the answer is:
lay on
'supply' is the definition.
Although both the answer and definition are verbs in their base form, I cannot understand how one could define the other.
'that supports a us city' is the wordplay.
'that' becomes 'yon' (archaic term meaning 'that').
'supports' says to put letters next to each other (bottom letters provide a support for the top ones).
'a us city' becomes 'LA' (short for Los Angeles).
'yon' after 'la' is 'LAY ON'.
Can you help me to learn more?
(Other definitions for lay on that I've seen before include "Provide (something)" , "instruction for Macduff" , "Provide (food, etc)" .)