1
general::
Also, of little or no avail. Of no use or advantage, ineffective, as in All his shouting was to no avail; no one could hear him, or The life jacket was of little or no avail. This idiom uses avail in the sense of "advantage" or "assistance," a usage dating from the mid-1400s. Also see TO LITTLE PURPOSE.
American Heritage Idioms
2
general::
Phrase(s): to no avail [and] of no avail
Cliché with no effect; unsuccessful. • All of my efforts were to no avail. • Everything I did to help was of no avail. Nothing worked.
McGrawhill's American Idioms And Phrasal Verbs