Serious notice in front of shelter (7)
I believe the answer is:
earnest
'serious' is the definition.
(similar in meaning)
'notice in front of shelter' is the wordplay.
'notice' becomes 'ear' (I've seen this in other clues).
'in front of' says to put letters next to each other (some letters go in front of others).
'shelter' becomes 'nest' (I've seen this in another clue).
'ear'+'nest'='EARNEST'
(Other definitions for earnest that I've seen before include "Serious, solemn" , "Pledge - far from frivolous" , "See 1" , "money put down" , "Sincere, solemn" .)