Abarim Publications' online Biblical Hebrew Dictionary
The root-verb פתה (pata) is thought to mean to be spacious, wide or open, but, as BDB Theological Dictionary chivalrously submits, the relationship between this root and its derivatives, which all have to do with being simple and easily persuaded, is not very well understood.
BDB suggests it may be because simple-minded people are open for all kinds of enticements, but here at Abarim Publications we surmise that this verb expresses the kind of feeble footing one may expect from the flats of swampy mud that exists between water (total ignorance) and dry land (full understanding). In fact, it seems that the primary usages of this verb describe the mental equivalent of the slowly growing of landmass by means of sedimentation:
In Genesis 9:27, Noah wishes that God יפת ליפת (yapet le yapet), or "make wide Japheth" (twice the same word). With the memories of the great flood still fresh and haunting, Noah reviews the general qualities of his three sons (which obviously describe the three great categories of human mentality, manifested in the many various wisdom traditions; see our article on the name Noah), and Japheth will be the son of the muddy transition.
Proverbs 20:19 and 24:28 urge the reader to not be or associate with one who pata his שפה (sapa, meaning lip or speech). These sayings probably employ a colloquial expression that describes someone who blabbers about things he knows little about and makes up the details he misses, which thus results in speech as solid as mud. Note that the word שפה (sapa, meaning lip, has the appearance of belonging to a cluster of words that all have to do with a phase of transition (as is סוף, suph, denoting the reeds that grow on the border between water and dry land).
This verb's only derived noun, the masculine פתי (peti) means simplicity, or a being "muddy of mind," where dry land denotes true understanding and water total ignorance. It occurs only in Proverbs 1:22: "How long, simple ones (פתים, petim), will you love simplicity (פתי, peti)?".
From this noun comes the denominative verb פתה (pata), which is identical to the root-verb, and some lexicons (HAW Theological Wordbook of the Old Testament for instance) make no distinction between the two. But whether this verb is separate or the same as the root-verb, it means to be simple or foolish (Job 5:2, Hosea 7:11). People that display the behavior described by this verb are easily persuaded (Exodus 22:16, Hosea 2:16) or deceived (2 Samuel 3:25, Proverbs 24:28).
Also see the verb פתח (patah I) meaning to open.