Many ancient texts were lost in war, and only their titles survive.
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佚 is literary and bound. The 'lost text' sense lives in 佚失 (lost) and 佚名 (anonymous; author lost); the 'at ease / reclusive' sense overlaps with 逸. It is also a rare surname.
Right side 失 (to lose) is the sound element, shifting from shī to yì, and its 'lose' meaning chimes neatly with the 'lost text / missing' sense — so it serves as both sound and a faint meaning hint.