gnome-dictionary: 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/gnome-dictionary - from package: gnome-utils

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

On Debian possible default full paths are:

/usr/bin/gnome-dictionary - from package: gnome-dictionary

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

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