Abarim Publications' online Biblical Hebrew Dictionary
The root צרע (sr') isn't used in the Bible as verb, but comparable roots in cognate languages mean to throw down or humble oneself. But it must have existed in Biblical times because the following derivations remain:
- The feminine noun צרעת (sara'at), denoting a skin disease commonly referred to as leprosy but actually covering a wide range of dermal afflictions (Deuteronomy 24:8, Leviticus 13:2), or even certain malevolent contaminations of clothing (Leviticus 13:47) or a house (Leviticus 14:34). BDB Theological Dictionary suggests that the latter two applications of our noun refer to some fungus or mould.
It should be noted that not the disease itself but the speckled skin as a result was considered unclean. If someone developed a skin diseases in patches, he was considered unclean, but if the disease grew until it covered that entire person, and the person was of one color again, he was considered clean (Leviticus 13:13). The Hebrew sanitary and hygiene laws were unique in the region and millennia ahead of their time, but it's quite possible that the lost Hebrew root-verb of this noun had something to do with ambiguity, much rather than with being humbled or getting ill.
- The denominative verb צרע (sara), meaning to be diseased of skin or to be leprous (Leviticus 13:44, 2 Chronicles 26:20).
- The collective feminine noun צרעה (sirah), meaning hornets. This curious word is used only to describe some mysterious force that God sends against the enemies of Israel (Exodus 23:28, Deuteronomy 7:20). BDB Theological Dictionary appears to propose that this is because this creature topples nations ("? as in wounding, prostrating"), but perhaps it's rather because the hornet has a bicolored skin.