Crossword Genius

It's essential to back up some relatives (5)

Ross

I believe the answer is:

vital

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

'it's essential' is the definition.
(similar in meaning)

'back up some relatives' is the wordplay.
'VITAL' is hidden backwards in amongst the letters.
However, I am unsure how this is indicated.

'to' acts as a link.

Can you help me to learn more?

(Other definitions for vital that I've seen before include "Are such statistics" , "Of the greatest importance" , "Essential for life; key" , "Critical, necessary" , "alive" .)

I've seen this clue in the Evening Standard.
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