Support headmaster escaping tsunami's destruction (7)

I believe the answer is:

sustain

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'support' is the definition.
(I know that support can be written as sustain)

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for sustain that I've seen before include "Provide nourishment" , "Bear (something's weight)" , "Withstand" , "Feed, nourish" , "Support, keep going" .)

I've seen this clue in the Sydney Morning Herald.

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