thesaurus2tex: 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/thesaurus2tex - from package: libbiblio-thesaurus-perl

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

Error in other languages:
thesaurus2tex: bevel nie gevind nie
thesaurus2tex: comandă negăsită
thesaurus2tex: comando não encontrado
thesaurus2tex: commande introuvable
thesaurus2tex: command not found
thesaurus2tex: käsku ei ole
thesaurus2tex: không tìm thấy lệnh
thesaurus2tex: komanda nerasta
thesaurus2tex: Kommando nicht gefunden.
thesaurus2tex: kommandot finns inte
thesaurus2tex: komut yok
thesaurus2tex: nie znaleziono polecenia
thesaurus2tex: níor aimsíodh an t-ordú
thesaurus2tex: no se encontró la orden
thesaurus2tex: no s'ha trobat l'ordre
thesaurus2tex: opdracht niet gevonden
thesaurus2tex: parancs nem található
thesaurus2tex: perintah tidak ditemukan
thesaurus2tex: príkaz nenájdený
thesaurus2tex: příkaz nenalezen
thesaurus2tex: команда не найдена
thesaurus2tex: командата не е открита
thesaurus2tex: 命令找不到
thesaurus2tex: コマンドが見つかりません