wn: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/bin/wn - from package: wordnet

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/wn - from package: wordnet

You may install the required package with command apt-get install {package}

Error in other languages:
wn: bevel nie gevind nie
wn: comandă negăsită
wn: comando não encontrado
wn: commande introuvable
wn: command not found
wn: käsku ei ole
wn: không tìm thấy lệnh
wn: komanda nerasta
wn: Kommando nicht gefunden.
wn: kommandot finns inte
wn: komut yok
wn: nie znaleziono polecenia
wn: níor aimsíodh an t-ordú
wn: no se encontró la orden
wn: no s'ha trobat l'ordre
wn: opdracht niet gevonden
wn: parancs nem található
wn: perintah tidak ditemukan
wn: príkaz nenájdený
wn: příkaz nenalezen
wn: команда не найдена
wn: командата не е открита
wn: 命令找不到
wn: コマンドが見つかりません