From 物(もの) (mono) + 忘(わす)れ (wasure, “連(れん)用(よう)形(けい) (ren'yōkei, “stem or continuative form”) of the verb 忘(わす)れる (wasureru).”).
ものわすれ • (monowasure) ←ものわすれ (monowasure)?