The first is a reduplicated and contracted form of the second (which occurs only as an alternate in certain tenses); probably akin to G4072 through the idea of alighting; to fall (literally of figuratively): - {fail} fall ({down}) light on.
From G4102; to have faith ({in} {upon} or with respect {to} a person or {thing}) that {is} credit; by implication to entrust (especially one´ s spiritual well being to Christ): - believe ({-r}) commit (to {trust}) put in trust with.
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Act 13:14¶ But when they departed from Perga, they came to Antioch in PisidiaG4099, and went into the synagogue on the sabbath day, and sat down.