First to observe a relative haven (5)
I believe the answer is:
oasis
'haven' is the definition.
('oasis' can be a synonym of 'haven')
'first to observe a relative' is the wordplay.
'first to' says to take the initial letters.
'relative' becomes 'sis' (short for sister).
The first letter of 'observe' is 'o'.
'o'+'a'+'sis'='OASIS'
(Other definitions for oasis that I've seen before include "Fertile spot in desert" , "Fertile place in a desert, a watering hole" , "Famous group" , "place of refuge" , "flower arranging stuff" .)