衿元[erimoto] front of neck
衿足[eriashi] nape of neck
衿裏[eriura] lining of the collar
半衿[haneri] neckpiece (on a kimono)

衿芯[erishin] collar core (stiff fabric, etc. inside a collar)
衿下[erishita] usu. the drop between collar and bottom hem on kimono, yukata, etc.
衿先[erisaki] collar points