It's essential to back up some relatives (5)
I believe the answer is:
vital
'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" .)