The American Heritage® Dictionary of the English Language: Fourth Edition. 2000.
Appendix I
Indo-European Roots
ENTRY:
pet-
DEFINITION:
To spread. Oldest form *pet2-. Derivatives include fathom, patent, and compass. 1. Suffixed o-grade form *pot()-mo-.fathom, from Old English fæthm, fathom, from Germanic *fathmaz, “length of two arms stretched out.” 2. Suffixed (stative) variant zero-grade form *pat--.patent, patulous, from Latin patre, to be open. 3. Probably variant zero-grade form in remade nasalized form *pat-no-.pace1, pandy, pas, paseo, pass, passé, passim; compass, expand, pasqueflower, passacaglia, passage1, passage2, passport, repand, spawn, from Latin pandere (past participle passus < *pat-to-), to spread out. 4. Suffixed form *pet-alo-.petal, from Greek petalon, leaf. 5. Suffixed form *pet-ano-.paella, pan1, paten, patina1, patina2, from Greek patan (? < *petan-), platter, “thing spread out.” 6.petasos, from Greek petasos, broad-brimmed hat, from Greek suffixed form *peta-so-. (Pokorny 1. pet- 824.)
-
-. patent, patulous, from Latin pat
-), platter, “thing spread out.” 6. petasos, from Greek petasos, broad-brimmed hat, from Greek suffixed form *peta-so-. (Pokorny 1. pet- 824.) 
