This article deals with the word stock of private letters written in an Old Germanic language, Old Frisian, is introduced also most notable word-building trends identi¬fied in the investigated data are presented. The phenomenon of “frisianizing” borrowed words is touched upon in this paper as well. Other specific features of Old Frisian illus¬trated here are dialectological differences and word form distortion cases, as well as the process of elision. One third of the Old Frisian word stock are compound words, therefore special atten¬tion is paid to compounding as a lexical tool used to produce new concept denotations. In terms of compounding, the most numerous and representative word classes are re¬searched: nouns, verbs and adverbs.