I didn't know the etymology of this word before. Quote below mentions "Armbrust".
"Brust " is German for "breast" or in this case shoulder.The crossbow had a stock that
prededed the musket stock, and was held against the shoulder for aiming.

Arbalest: (Fr: arbalète, Ger. Armbrust, Crossbow) The correct term for a crossbow, introduced
early in the 14th century. The crossbow consisted of a bow mounted on a stock that could be
cranked or pulled into place using more leverage than could be used on a conventional longbow.
The result was a very high-powered, lower trajectoried weapon of great destructive potential. It
fired a bolt, a shorter version of an arrow. However, the firing time on a crossbow was slow
compared to the longbow, and for that reason and owing to the vastly higher expense during the
period, the longbow remained the favored missile weapon of the 14th and 15th century in England
and in France. From time to time the crossbow was banned by various laws, but it remained a
weapon of great popularity during the late 14th century in the low countries, the Swiss states, in
Germany and in Italy