Synonyms for Guileless (same or very similar meaning)
WordNet sense 1 (free of deceit):
transparent
WordNet sense 2 (characterized by honesty and fairness):
square, straight
WordNet sense 3 (free from guile):
honest
WordNet sense 4 (simple and natural; without cunning or deceit):
artless
From the ODE community, based on WordNet
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