Based on a Goldogrin (Sindarin's "draft") verb, laitha- "to let slip, lose, mislay, forget...", which undoubtedly survived in Sindarin with slight alterations to its sense and form, as leitha- "to release, set free". Thus, one could simply use leitha- for "to forget", but in order to avoid overburdening the verb, leg- as a neologism could be preferred.
Another method to get "to forget" is updating the early draft verb only phonetically as laetha-, which basically creates a root rather than a derivation as "LAYATH", and this does not work as an extension of LAY "flourish" (cf. LAYAK "fresh"). Yet another approach is to combine dan with ren- as *dadhren-, which arguably means "to remember back" instead.
A direct derivation from √LEK.
Based on a Goldogrin (Sindarin's "draft") verb, laitha- "to let slip, lose, mislay, forget...", which undoubtedly survived in Sindarin with slight alterations to its sense and form, as leitha- "to release, set free". Thus, one could simply use leitha- for "to forget", but in order to avoid overburdening the verb, leg- as a neologism could be preferred.
Another method to get "to forget" is updating the early draft verb only phonetically as laetha-, which basically creates a root rather than a derivation as "LAYATH", and this does not work as an extension of LAY "flourish" (cf. LAYAK "fresh"). Yet another approach is to combine dan with ren- as *dadhren-, which arguably means "to remember back" instead.