The King James Version (and perhaps others) confounds the English translation in this respect.
Using Blue Letter Bible, I performed a word search for "devil" in the King James Version, and it "occurs 61 times in 57 verses in the KJV." According to its lexicon search, three nouns are translated as "devil" in the King James Version:
G1140 δαιμόνιον (daimonion)
G1228 διάβολος (diabolos)
- devil(s): 35/38
- false accuser(s): 2/38
- slanderer(s): 1/38
G1142 δαίμων (daimōn)
- devil(s): 59/60
- god(s): 1/60
Regarding the verses you cited, you simply need to use a site like Blue Letter Bible and identify the underlying Greek word. Then, read my analysis below.
The English Word "Devil"
The English word "devil" is basically a loose transliteration of the Greek word διάβολος. But, an actual translation (thereby capturing the meaning of the Greek word) would be "slanderer" or "accuser," since διάβολος is a noun derived from the verb διαβάλλω, meaning "to slander, accuse, defame." In any case, as long as one understands the meaning of διάβολος' etymological origin (i.e., the verb διαβάλλω), it's okay to translate it into English as "devil," just like we write "Messiah" and understand by it, "anointed one," although the word "Messiah" is also a loose transliteration, not a translation. In conclusion, the English noun "devil" is a loose transliteration of the Greek noun διάβολος, which may be translated into English as "slanderer, accuser."
In the Greek New Testament, the Greek word διάβολος is most often used in reference to one particular heavenly being who led a rebellion against God and was cast out of heaven along with his fellow apostate angels (cp. Rev. 12:9). However, it may also be used in reference to humans who slander (cp. 1 Tim. 3:11).
The English Word "Demon"
You may have already guessed that the English word "demon" is also a loose transliteration of the Greek words δαίμων and δαιμόνιον. But, very few know what a demon is. This confusion is compounded by the fact that the King James Version almost always translates both δαίμων and δαιμόνιον as "devil" and not "demon." So, if someone did not bother to examine the Greek, they would never know a distinction exists. In fact, I did a word search on "demon" in the King James Version, and it never occurs. This is rather unfortunate.
There are various theories on what a demon is, and unfortunately, I don't have the time to critique them all.
Luke 4:33 seems to place πνεῦμα ("spirit") in apposition to δαιμονίου ἀκαθάρτου ("unclean demon"), thereby suggesting that a demon is a spirit. Heinrich Meyer notes, "The genitive is a genitive of apposition or of nearer definition...and δαιμόνιον, which, according to Greek usage, is in itself applicable to either good or evil spirits, being used by Luke for the first time in this passage, is qualified by ἀκαθάρτου."1 Elsewhere, in the Book of Tobit, we find Asmodeus referred to as an "evil demon" (τὸ πονηρὸν δαιμόνιον).2 The same author also mentions a "demon or evil spirit" (δαιμόνιον ἢ πνεῦμα πονηρόν),3 again suggesting that "demon" is equated to "evil spirit."
However, the word "spirit" can refer to a few things, including the immaterial and incorporal essence within man, sometimes referred to as his rational soul (cp. Heb. 4:12; 1 Thes. 5:23).2 Or, it can refer to angels (Heb. 1:7 cp. Psa. 104:4). So, is a demon, being identified as a "spirit," the former or the latter?
Josephus also mentioned demons.5 But he apparently believed they were the disembodied spirits of wicked humans who died. He wrote,6
ἔστι δὲ μετὰ τοσούτων κινδύνων διὰ μίαν ἰσχὺν περισπούδαστος: τὰ γὰρ καλούμενα δαιμόνια, ταῦτα δὲ πονηρῶν ἐστιν ἀνθρώπων πνεύματα τοῖς ζῶσιν εἰσδυόμενα καὶ κτείνοντα τοὺς βοηθείας μὴ τυγχάνοντας, αὕτη ταχέως ἐξελαύνει, κἂν προσενεχθῇ μόνον τοῖς νοσοῦσι.
Yet, after so many dangers, it is greatly desired because of one power: for, it quickly expels those called "demons" (now, these are spirits of wicked men which enter those who are alive and kill those who do not obtain help), and only if it is brought to the sick people.
It is up to the reader to further investigate this matter in order to determine the exact nature of demons, but one thing is certain, there is a difference between (1) διάβολος and (2) δαίμων/ δαιμόνιον.
1 Commentary on Luke 4:33
2 Tobit 3:8, 3:17
3 Tobit 6:8
4 Compare Philo, Who is the Heir of Divine Things, §132: «τὴν μὲν ψυχὴν εἰς λογικὸν καὶ ἄλογον»
5 Jewish Antiquities, 6.8.2, 6.11.2, 8.2.5
6 Wars of the Jews, 7.6.3
Meyer, Heinrich. Critical and Exegetical Commentary on the New Testament.