Tiny relative has least (7)
I believe the answer is:
minimum
'least' is the definition.
(similar in meaning)
'tiny relative' is the wordplay.
'tiny' becomes 'mini'.
'relative' becomes 'mum' (mum is a kind of relative).
'mini'+'mum'='MINIMUM'
'has' is the link.
(Other definitions for minimum that I've seen before include "The least of smallest amount possible" , "Lowest point" , "Least recorded value" , "Least possible quantity" , "Nadir" .)