Abarim Publications' online Biblical Hebrew Dictionary
Scholars have identified three different Hebrew roots that are spelled and pronounced the same:
The verb עדר (adar I) is an Aramaic loan-word, which means to help and occurs only in 1 Chronicles 12:34. This verb is the Aramaic version of the familiar Hebrew verb עזר (azar), which is the root of names like Ezra, Eleazar and Ezer.
The verb עדר (adar II) means to hoe, and occurs in Isaiah 5:6 and 7:25. In the latter verse, the prophet Isaiah uses a noun derived from this verb: מעדר (ma'der), meaning a hoe.
Finally, the verb עדר (adar III) means to be lacking or fail (1 Samuel 30:19, Isaiah 40:26; none is missing, Zephaniah 3:5; God does not fail).
Oddly enough, this verb's only derivative is the word עדר (eder), meaning flock or herd. That renders the curious notion that the Hebrews saw a flock as something that lagged or loitered, but also as something that was characterized by elements that continuously went missing.
Jesus' parable of the lamb gone astray (Matthew 18:11-14, also see John 10:1-16) is therefore not only about the lamb that was found and saved but also about the herd as a whole. When Jesus is the shepherd, the entire flock changes its natural quality, from a collection of easy pickings to a firmly kept collective.