leo: 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 Debian possible default full paths are:

/usr/bin/leo - from package: libwww-dict-leo-org-perl

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

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