What is the technical definition of the word "Muslim"? Is there any other use of the word that is appropriate?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

The word Islam has two meanings: a general meaning and a specific meaning.

Its general meaning is sincerity, submission, obedience and surrender to Allah. Allah has described His Messengers and the best of His other people as incorporating these characters. Allah Says (what means): {Abraham was neither a Jew nor a Christian, but he was one inclining toward truth, a Muslim [submitting to Allah]. And he was not of the polytheists.} [Quran 3:67]. Allah also says about the Prophet Yoosuf (what means): {My Lord, You have given me [something] of sovereignty and taught me of the interpretation of dreams. Creator of the heavens and earth, You are my protector in this world and the Hereafter. Cause me to die a Muslim and join me with the righteous.} [Quran 12:101]. Also, Prophets Ibraheem (Abraham) and Ya'qoob (Jacob), may Allaah exalt their mention, ordered their sons to abide by Islam. Allah Says (what means): {And Abraham instructed his sons [to do the same] and [so did] Jacob, [saying], “O my sons, indeed Allah has chosen for you this religion, so do not die except while you are Muslims.”} [Quran 2:132]. Besides, Allah narrates about the disciples of ‘Eesa (Jesus) that they said: {And [remember] when I inspired to the disciples, “Believe in Me and in My messenger [i.e. Jesus].” They said, “We have believed, so bear witness that indeed we are Muslims [in submission to Allah].”} [Quran 5:111]

Allah also Says (what means) on the tongue of the queen of Sheeba {She said, “My Lord, indeed I have wronged myself, and I submit with Solomon to Allah, Lord of the worlds.”} [Quran 27:44]

The second meaning is worshipping Allah and submitting to Him by following the Sharee’ah conveyed by the Prophet Muhammad from his Lord. The Prophet Muhammad explained this meaning by saying: "Islam is to testify that none has the right to be worshipped but Allah, and that Muhammad is the Messenger of Allah, and to establish the prayer, pay the Zakaah, observe the Fast of Ramadan, and perform Hajj to the House of Allah if one is able to do so financially and physically.” [Al-Bukhari and Muslim]

It is this Islam that distinguishes a Muslim from a Jew or a Christian, so it is said the Muslims, the Jews, the Christians and the Maggi.

After the Prophecy of Muhammad with this message of Islam, the religion is restricted to Islam and is rejected from other than the Muslims. Allah Says (what means): {And whoever desires other than Islam as religion-never will it be accepted from him, and he, in the Hereafter, will be among the losers.} [Quran 3:85]. Besides, the Prophet said: “I swear by Him in Whose Hand my soul is, there is no Jew or Christian of this nation [i.e. from the time of the Prophet until the Day of Judgment] who hears about me and then dies without believing in what I was sent with, except that he will be amongst the people of Hellfire.” [Muslim]

Allah knows best.