Analogy

Analogy refers to a diachronic process which changes words after the model of other forms.

Examples
In Gothic, the stem of the noun meaning 'foot' is a so-called u-stem, i.e. a stem ending in a suffix -u, although originally this stem did not end in a suffix -u. Compare the nominative singular of the non-u-stem foot in Latin (pe:s), Ancient Greek (pó:s), Sanskrit (pá:t), and Gothic (fotus) with the nom.sg. of the u-stem son in Ancient Greek (hui&oacutes), Sanskrit (su:n&uacutes) and Gothic (sunus). The diachronic account of this class shift runs as follows. Historically, the accusative ending -m was syllabic after consonant-final roots. By a regular sound change this syllabic /m/ became -um in Germanic. Hence, the accusative of foot became fot-um. The result of this change was that the accusative fotum became indistinguishable from the accusative of u-stems (e.g. sunum), although their underlying morphological structure was different: fot-um vs. sun-u-m. If one assumes that the accusative fot-um is reanalyzed as fot-u-m, the change *fot > fotus (nom.sg.) can be schematized as sun-u-m:sun-u-s = fot-u-m:X, where X is fot-u-s.

Link
Utrecht Lexicon of Linguistics