As I understood, the function of this dictionaries are the same, except that Synonyms Dict do not support operation with phrases.
Is It OK to use one dictionary for thesaurus and phrases in PostgreSQl full text search?
my_custom.ths
# synonyms
postgres : pgsql
postgresql : pgsql
postgre : pgsql
gogle : googl
# phrases
indices : index*
supernovae stars : sn
crab nebulae : crab