Abarim Publications' online Biblical Hebrew Dictionary
Dictionaries list two roots of the form רדה (rada) and one of the form רדד (radad). They are not commonly reported to be etymologically related, but their meanings overlap to such an extent that the "two" verbs רדה (rada) are clearly not two but one, and in turn so alike רדד (radad) that the former might as well be considered a by-form of the latter. Similarly, these verbs all clearly have forms and applications in common with the verb ירד (yarad), meaning to go down.
All three of the following word-clusters have to do with a spreading out or overwhelming with the express objective of drawing produce:
The root-verb רדד (radad) primarily denotes applying a protective cover, and secondarily to draw some kind of produce from whatever is protected. Hence gold was spread out over wood carvings (1 Kings 6:32, here the form ירד is used), and Cyrus was the YHWH's anointed, whose reign covered nations and loosened the loins of kings and opened doors (Isaiah 45:1).
Likewise and for the same reason the Lord placed David's people under him (Psalm 144:2). In Judges 19:11 appears the enigmatic statement of the day being "spread fully," that is to say: whatever could be drawn from that day had been drawn; the productive part of the day had been fully utilized and was exhausted.
This verb yields one derivative, namely the masculine noun רדיד (redid), denoting a wide cape or veil of some sort (something that covers). This noun occurs in Song of Solomon 5:7 and Isaiah 3:23 only.
The root-verb רדה (rada I) is usually employed in the Bible in the meaning of to have dominion, to rule (Genesis 1:28, Ezekiel 29:15). But the nature and objective of this ruling are shown by this verb's usage in Joel 4:13, where the prophet says, "Come! Tread! For the winepress is full . . . "
This verb is obviously associated to the verb רדד (radad), and most likely also to the verb ירד (yarad), meaning to go down, or (in this case), cause to go down. The form ירד used in Judges 5:13, for instance, is commonly thought to derive from our verb רדה, rada). And in Psalm 72:6, the form ירד is commonly translated with 'may he come down [like rain]', whereas two verses later, in 72:8, the same form is translated with 'may he rule'.
In some manuscripts Isaiah 14:6 contains the noun מרדה (merada), which would mean dominion, but most manuscripts have the noun מרדף (murdap — from the verb רדף (radap) — which means persecution.
The root-verb רדה (rada II) means to scrape out. It's used only once in the Bible: in Judges 14:9, Samson scrapes out honey from the lion's carcass. Since Samson obviously subdued the lion first, here at Abarim Publications we see no reason to maintain that there are two separate roots רדה (rada).
In Jeremiah 5:31 the priests are engaged in some illicit action, which some commentators suggest may be scraping out whatever pots and pans (and hands giving them gifts, etc) they like. Most scholars, however, take this occurrence of רדה (rada) from the previous root: the priests rule in whatever way they want. Here at Abarim Publications we see no difference.