From Wiktionary, the free dictionary
didis (“large”) + -yn (“forms adverbs indicating a change toward a condition”)
didyn
- up in size; becoming larger
- Antonym: mažyn
1919 July 30, Draugas[1], volume 4, number 178, Chicago:Riaušes Chicagoje eina didyn- The riots in Chicago are on the rise [getting bigger]