A sign of spring — family eat outside house at last (9)
I believe the answer is:
celandine
'a sign of spring' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.
'family eat outside house at last' is the wordplay.
'family' becomes 'clan' (clan can mean a large family).
'eat' becomes 'dine' (to dine is to eat a meal).
'outside' is an insertion indicator (some letters go outside others).
'at last' indicates one should take the final letters.
The final letter of 'house' is 'e'.
'clan'+'dine'='clandine'
'clandine' enclosing 'e' is 'CELANDINE'.
Can you help me to learn more?
(Other definitions for celandine that I've seen before include "Flowering plant - decennial (anag)" , "Plant of buttercup family" , "... one blooming" , "Land niece with the swallowwort." .)