Spontaneous Aunt travelled by rail wanting independence (7)
I believe the answer is:
natural
'spontaneous' is the definition.
(synonyms)
'aunt travelled by rail wanting independence' is the wordplay.
'travelled' indicates anagramming the letters.
'by' says to put letters next to each other.
'wanting' suggests deleting specific letters (to want something can mean to lack it or need it).
'independence' becomes 'i'.
'rail' with 'i' taken out is 'ral'.
'aunt' is an anagram of 'natu'.
'natu'+'ral'='NATURAL'
(Other definitions for natural that I've seen before include "Illegitimate" , "Ordinary" , "person regarded as certain to qualify" , "Innate, inborn" , "Unsophisticated" .)