I want to show a use of tuus that baffled me, and my proposed solution.
Context: In Metamorphoses, Book 13, line 210 f., Ulysses continues to brag about his war record, while disparaging that of Ajax. First Ulysses notes that for the first nine years the Trojans kept within their walls, with little opportunity for open battles. Then he addresses Ajax.
quid facis interea, qui nil nisi proelia nosti? 210
quis tuus usus erat?
Translation:
What do you do meantime, you who knew nothing except battles?
What was your contribution?
quis: interrogative pronoun
tuus: nominative, masculine, singular, possessive adjective, modifies usus
usus: noun, nominative singular, modified by tuus