Father's leading wise man's lobby (7)
I believe the answer is:
passage
'lobby' is the definition.
(thesaurus)
'father's leading wise man's' is the wordplay.
'father's' becomes 'pas' (pa is a kind of father).
'leading' says to put letters next to each other.
'wise man' becomes 'sage' (sage is a kind of wise man).
'pas'+'sage'='PASSAGE'
(Other definitions for passage that I've seen before include "Book extract; transit" , "crossing" , "Sea/air journey" , "Section of text; journey" , "Piece of writing" .)