Abarim Publications' online Biblical Hebrew Dictionary
The occurrences of the verb פער (pa'ar) indicate adjunction with strong passion or feeling, usually not very positive (Job 16:10, Isaiah 5:14, Job 29:23), and describe the wide opening of the mouth, hence perhaps alluding to other body cavities. The Psalmist uses this verb in a positive way: a wide opening of the panting "mouth" of someone longing for God's commandments (Psalm 119:131).
Apart from two or three names, this verb has no derivatives. The fact that there is no noun meaning "opening," suggests that this verb does not so much describe the normal functioning of a body cavity but rather the motivations behind opening wide: a yearning to be filled.