My newest project, piled on top of about 8 others, is to write on cards all the foreign roots and foreign derivative affixes in Urdu so as to guess the meanings of new words from their etymologies. That would be like getting one of those books on Latin and Greek roots with some French thrown in to help one guess as to the meaning of words like ‘supplemental’. That can be misleading as the words’ meanings often change drastically from one language to another and from one era to another.
I was responding to an item on another language related blog when I coined the term internal cognates, by which I mean words related to other words in the same language. By knowing one word and knowing how word building happens in the language, you can often come up with a reasonable meaning for a hitherto unknown word. It can be misleading, e.g. ‘fastness’ does not designate the quality of being fast but rather a kind of redoubt or stronghold in a fortified, remote area, although it also denotes the quality of swiftness. (I would never use it that way).
An easy example in another language is Urdu yadgar = monument, memorial, from Arabic yad = memory and Persian gar = making. (Note yad in Hebrew yad vashem, the memorial to the Holocaust; Hebrew and Arabic are closely related languages).