cbf94194_Euclid_5_Intro_html__Definitions
[0] 6. [Brief comments] The Greek word 'analogon' is formed from a prepositional phrase and is adverbial. 'Proportional' is the standard translation, but 'in-ratio' would be better. The difficulty is that one needs to be able to form the noun from the preposition, for 'analogia' (cf. def. 9), while 'in-rationality' or something like that is too artificial. [Definitions] 
and let magnitudes having the same ratio be called 'proportional',
Euclid.5.Intro.html
Definitions