IPA: /ˈɡaɪl.ləs.nəs/
KK: /ˈɡaɪləsnəs/
The quality of being honest and straightforward, without any deceit or trickery.
Her guilelessness made her a trustworthy friend.
Guilelessness is formed from "guile" (from Old French *guile*, meaning deceit or trickery) and "-lessness" (meaning without). The word describes a state of being without deceit or trickery, embodying innocence and honesty.
Think of being 'without' ('-lessness') 'deceit' ('guile') — that's why guilelessness means being innocent and honest.