Additional note to Sparteye's excellent etymology (and I parbly don' need to tell most of you this). The Classical Greek phi was not an unvoiced labio-dental fricative nor even an unvoiced bilabial fricative but rather an unvoiced aspirated bilabial plosive (the pi was an unvoiced unaspirated bilabial plosive). Thus Pelistim and Philistinoi were not that far apart, phonetically.