The comparative of adjectives is formed by addition of the suffix -iz or -óz between the stem and case ending. The superlative is derived by addition of the suffix -st or -óst between the stem and case ending.

þ>d  after vowels.

As with the positive degree, the superlative degree declines either strong or weak according to the requirements of context. The superlative, however, does not take the alternate pronominal ending -ata in the neuter singular nominative or accusative. The comparative, by contrast, only assumes weak adjectival endings, regardless of context. The only difference between comparative endings and general weak adjectival endings occurs in the feminine: the feminine declines like the īn-stem managei, rather than tuggo. The adjective júhisa 'younger', from juggs 'young', serves to illustrate comparative declension.

Several adjectives are members of suppletive systems, whereby the positive forms derive from a base different than that of the comparative and superlative. A few of the most common such adjectives appear below. The superlative sinista generally translates Greek presbúteros 'elder': þái sinistans 'the elders'.

Intensive adjectives are formed by addition of the ending -(t)uma. These formations inflect like comparatives, but they generally do not mark any specific comparison. These have a superlative formed by adding -(t)umist between the stem and case ending.

* hypothetical, but implied.

Compare af-tuma to Lat. op-timus, as well as in-timus and Sanskrit án-tamas. Likewise compare the formation of ordinals such as Lat. septimus, Sanskrit saptamás.

The dative case is used in conjunction with a comparative to denote the standard of reference or comparison, as denoted by the Modern English 'than'. For example, swinþo mis 'mightier than me'.

http://www.utexas.edu/cola/centers/lrc/eieol/gotol-4-X.html#Got04_GP17_02