adj. 25B6; adjective
it is improper for policemen to accept gifts : INAPPROPRIATE, unacceptable, unsuitable, unprofessional, irregular; unethical, corrupt, immoral, dishonest, dishonourable; informal not cricket.
it was improper for young ladies to drive a young man home : UNSEEMLY, indecorous, unfitting, unladylike, ungentlemanly, indelicate, impolite; indecent, immodest, immoral.
an extremely improper poem : INDECENT, risqué, off colour, suggestive, naughty, ribald, earthy, smutty, dirty, filthy, vulgar, crude, rude, obscene, lewd; informal blue, raunchy, steamy; Brit. informal fruity, saucy.
acceptable, decent.