Final answer:
To derive a stem of a third declension word, find the genitive singular and drop the ending. When combining stems with suffixes starting with e, i, or y, final e's are usually deleted as these vowels keep the preceding consonant soft.
Step-by-step explanation:
To derive the stem of any third declension word, find the genitive singular, and drop the ending. For example, when combining gallery with the suffix i + es, we get galleries, where the letter e in the suffix es is marked to indicate the sound [u0113]. Similarly, for hurry + i + es, we get hurries; marry + i + es becomes marries; study + i + es turns into studies (where the final u201cdyu201d in the stem study is replaced by iu201d to form study + i + es), and vary + i + es changes to varies. Note that if the suffix starts with an e, i, or y, such as in lacy + est, the final e in lacy is deleted as in laciest, effectively showing that the final e is not needed to keep the c soft.