Abarim Publications' online Biblical Hebrew Dictionary
The root בדד (badad) occurs all over the Semitic language area and signifies separation, isolation and more specifically the formation of a singular identity from a pinched off subset of a larger continuum. As a verb it may mean to disunite or divide into parts, or to go alone or act independently. It's used in the Bible a mere three times: and Psalm 102:7 speaks of a bird perched lonely on a house top, Isaiah 14:31 of a straggling soldier, and Hosea 8:9 of a wandering solitary donkey.
The derived masculine noun בדד (badad) means isolation, separation or exclusivity. It occurs more often than the verb and may speak of dwelling in isolation because of quarantine (Leviticus 13:46), mourning (Lamentations 1:1) or a quest for safety from violation (Numbers 23:9, Deuteronomy 33:28, Jeremiah 49:31). This noun may speak of a place or condition of untouchability where God places his people (Micah 7:4), or it speaks of the exclusivity of God to lead his people to safety (Psalm 4:8). Deuteronomy 21:12 reads: "The Lord alone led him; no foreign god was with him." Likewise Jeremiah 15:17 reads, "Because of Your hand upon me I sat alone, for You filled me with indignation."
The much more common masculine noun בד (bad), likewise, describes separation. It very often occurs in conjunction with the prefix ל (le), to or onto, to form לבד (lebad), meaning by itself, by himself or by themselves (Exodus 26:9, Judges 7:5, Isaiah 5:8). The famous statement of Genesis 2:18, "It is not good for the man to be by himself" uses לבד (lebad). Significantly, however, this noun does not so much describe a complete severance from its maternal medium but rather the formation of an identifiable entity within it. Our noun בד (bad) often occurs to mean part or part of, suggesting that there are more parts and that all these distinct parts together make up an integrated whole (Exodus 30:34, Job 18:13, Ezekiel 17:6).
Some scholars identify a second but identical noun בד II (bad II), which others (including us here at Abarim Publications) surmise is rather a specialized usage of בד I (bad I). It denotes the signature white linen ephod of the priestly class of Israel (Exodus 28:42, Leviticus 16:4): Samuel wore one (1 Samuel 2:18), David wore one (2 Samuel 6:14) and angels show up in them too (Ezekiel 9:2-3, 10:2, 10:6).
A third identical noun בד III (bad III), which may in fact again be the same one used specifically, describes speech that is notably separate from common human discourse: idle talk (Job 11:3, Isaiah 16:6) or empty talkers (Isaiah 44:25, Jeremiah 50:36). Note that the familiar Greek word ιδιωτης (idiotes) expresses a similar idea and literally means "in a category of their own".
The verb בדא (bada') may have nothing to do with the previous (as scholars assume) but it may also be a continuation of the concept expressed in בד III (bad III). It means to connive (Nehemiah 6:8) or vainly invent (1 Kings 12:33), and is used these mere two times.