Crossword Genius

Only a fluctuating supply (3,2)

Ross

I believe the answer is:

lay on

I'm a little stuck... Click here to teach me more about this clue!

'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.

'only a fluctuating' is the wordplay.
'fluctuating' is an anagram indicator.
'only'+'a'='onlya'
'onlya' anagrammed gives '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)" .)

I've seen this clue in The Globe and Mail.
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