Take lead off vizsla wagging tail — essential (5)
I believe the answer is:
vital
'essential' is the definition.
(similar in meaning)
'take lead off vizsla wagging tail' is the wordplay.
'take lead off' indicates taking the first letters (the letter which 'leads' the word).
'wagging' indicates an anagram (I've seen this in other clues).
The first letter of 'vizsla' is 'v'.
'tail' anagrammed gives 'ital'.
'v'+'ital'='VITAL'
(Other definitions for vital that I've seen before include "Critical; life-sustaining" , "Critical, necessary" , "Essential; lively" , "Crucial" , "alive" .)