Abarim Publications' online Biblical Hebrew Dictionary
There are two separate roots תפל (tapal), which meanings aren't all that far apart:
The verb תפל (tapal I) is used only once, in 2 Samuel 22:27, where it means to show oneself unsavory (or tasteless, quite literally; in modern Hebrew this word means unsalted. Also see Matthew 5:13).
Derivatives of this root are:
- תפל (tapel), an adjective literally meaning tasteless or unseasoned but foolish by implication (Lamentations 2:14 and Job 6:6).
- The feminine variant תפלה (tipla), occurs in Job 1:22 and 24:12, and Jeremiah 23:13, and again means folly or moral unsavoriness.
The unused and untranslatable root תפל (tpl II) yields the derivation תפל (tapel), meaning whitewash (Ezekiel 13:10-15 and 22:28).
Another word of interest is תפלה (tepilla), meaning prayer, from the verb פלל (palal) meaning to intervene or pray.