The musical term that means to slow tempo is ritardando. If you'd like to slow the tempo very quickly you'd call it a molto ritardando.
Ritardando is a musical term meaning to gradually slow down in tempo.
"Largo" is a slow, plodding, heavy tempo - like the marching of elephants.
The Italian musical term for a cheerful or fast tempo is "Allegro."
The proper musical term for increasing the tempo is "accelerando."
moderato e grazioso
rit. or ritard.
The purpose of using the musical term "retard" in a piece of music is to indicate that the tempo should slow down gradually.
Andante is a musical term used to mean "at a moderately slow pace", usually approximated to "walking pace".
Lento or Ritardando
The terms "ritardando" and "rallentando" are both used to signify a gradually decreasing tempo.
The tempo marking, usually located near the top of the music composition, determines how many beats pre minute the pace of the song should be played at. You should use a metronome to determine this.
The correct musical term for decreasing the tempo in a piece of music is "ritardando."