We argue that there is a diachronic process, distinct from phonological erosion, that results in the loss of inflectional morphology that is trapped when a clitic attaches to a host, becoming an affix. This is supported with attested examples from Mainland Scandinavian, Georgian, Spanish, and Greek, as well as shallow, well-accepted reconstructions from Slavic and Georgian. It is further supported by new reconstructions from Zoque (Mixe-Zoquean) and Andi (Northeast Caucasian). For example, in Old Norse the postposed article is a clitic, and there is a case ending between the noun stem and the article: hest-s=in-s ‘the horse (gen)’. The first s is trapped morphology, and it is subsequently lost: hest-en-s. Similarly, in pre-Georgian, the postposed article traps the ergative case marker, *-n: *k'ac-n=ma-n ‘the man (erg)’; it is subsequently lost: k'ac-man. We argue that the loss of trapped morphology is not sound change or another phonological process, but a morphological process.