Theory definitions go go!

accelerando

becoming quicker

accent

a stressed note

ad libitum

at the liberty of the performer

adagio

slow

agitato

agitated

alla

in the manner of

allargando

broadening, becoming slower

allegretto

fairly fast (a little slower than allegro)

allegro

fast

andante

moderately slow; at a walking pace

andantino

a little faster than andante

animato

lively, animated

arco

on a bowed string instrument, resume bowing after a pizzicato passage

a tempo

return to the original tempo

attacca

proceed without a break

ben

well

bewegt

moving

calando

becoming slower and softer

cantabile

in a singing style

cédez

yield; hold the tempo back

col

with

comodo

at a comfortable, easy tempo

con brio

with vigor, spirit

con espressione

with expression

con fuoco

with fire

con grazia

with grace

con moto

with motion

con sordino

with mute

crescendo

becoming louder

da capo

from the beginning

dal segno

from the sign

D.C. al fine

repeat from the beginning and end at fine

decrescendo

becoming softer

dolce

sweet, gentle

dolente

sad

e

and

espressivo

expressive, with expression

fine

the end

forte

loud

fortepiano

loud, then suddenly soft

fortissimo

very loud

giocoso

humorous, jocosely

grandioso

grand, grandiose

grave

slow and solemn

grazioso

graceful

langsam

slow, slowly

largamente

broadly

larghetto

fairly slow, but not as slow as largo

largo

very slow

legato

smooth

léger

light, lightly

leggiero

light, nimble, quick

lentement

slowly

lento

slow

l’istesso tempo

the same tempo

loco

return to the normal register

ma

but

maestoso

majestic

mano destra

right hand

mano sinistra

left hand

marcato

marked or stressed

martellato

strongly accented, hammered

mässig

moderate, moderately

meno

less

meno mosso

less movement, slow

mesto

sad, mournful

mezzo forte

moderately loud

mezzo piano

moderately soft

mit Ausdruck

with expression

moderato

at a moderate tempo

modéré

at a moderate tempo

molto

much, very

morendo

dying, fading away

mouvement

tempo, motion

non

not

ottava

an octave higher

pedale

pedal

pesante

weighty, with emphasis

pianissimo

very soft

piano

soft

più

more

più mosso

more movement (quicker)

pizzicato

on a bowed string instrument, pluck the string instead of bowing

poco

little

poco a poco

little by little

prestissimo

as fast as possible

presto

very fast

primo

first; the upper part of a duet

quasi

almost, as if

quindicesima alta

two octaves higher

rallentando

slowing down

risoluto

resolute

ritardando

slowing down gradually

ritenuto

suddenly slower, held back

rubato

with some freedom of tempo to enhance musical expression

scherzando

playful

schnell

fast

secondo

second; second or lower part of a duet

sehr

very

semplice

simple