Concise Bible Dictionary:
The words βραδύς, νωθρός, and ἀργός have similar meanings. βραδύς occurs but three times in the N. T.; it differs from the other words in that it is used in a good as well as a bad sense, having only reference to time: 'slow,' in the sense of tardy. The Lord said, "O fools, and slow of heart to believe all that the prophets have spoken," Luke 24:25; but in Jas. 1:19 the exhortation is "be swift to hear, slow to speak, slow to wrath."
νωθρός seems to imply more habitual slothfulness. It occurs but twice in the N. T. The Hebrew saints were "dull of hearing" when they ought by diligence to have been teachers, Heb. 5:11; and are exhorted not to be ‘slothful,' but followers of those that inherit the promises. Chap. 6:12. It occurs once in the LXX: it is not fit that one diligent in business should attend on slothful men, Pro22:29.
ἀργός (perhaps from ἀεργός, a neg., and ἔργον, work ') differs from the above in that it is applied to things as well as to persons, and involves blameworthiness. In Matt. 12:36, "every ‘idle' word that men shall speak" will have to be accounted for. It is translated ‘idle' in Matt. 20:3, 6, 6; 1 Tim. 5:13, 13. In Titus 1:12 The Cretans are said to be slow bellies,' or lazy gluttons.' In 2 Pet. 1:8, in "using all diligence".... they would be "neither idle nor unfruitful."
In the LXX ἀργός occurs in 1 Kings 6:7 (11), applied to the stones for the temple, but in what sense is not clear, unless it be that there was no
more work to be done upon them. Sir C. Brenton translates ‘rough hewn stones.'
Strong’s Dictionary of Greek Words:
Meaning:
from 1 (as a negative particle) and 2041; inactive, i.e. unemployed; (by implication) lazy, useless
KJV Usage:
barren, idle, slow