I was wondering how could I remove one (wrongly inserted) entry/word from the ispell private-dictionary.
EDIT
after more digging i am still unab
You should just be able to edit your personal dictionary file to remove the unwanted entry. The dictionary file is a text file, probably located at ~/.ispell_default, or ~/.ispell_[LANGUAGE], e.g. ~/.ispell_italian.
~/.ispell_default
~/.ispell_[LANGUAGE]
~/.ispell_italian