Something to hang on to when unseated (5)

I believe the answer is:

strap

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

'something to hang on to' is the definition.
(I've seen this before)

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

Can you help me to learn more?

(Other definitions for strap that I've seen before include "Parts (anag.)" , "Restraining fastener" , "loopy band" , "something to hang on to" , "Belt; leather strip" .)

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

Want a hint initially instead of a full solution? Install my app