As a (fourth declension masculine) noun, ūsus can adopt a variety of closely-related but powerfully particular meanings:
1. Ūsus + genitive typically refers to the use, exercise or enjoyment of something.
- ūsus ocūlōrum: eyesight
- ūsus pectōrālis : push-ups
- ūsus unguentis: the delights of cologne (I highly recommend getting this at TJ Maxx—half-price!)
2. On its own, ūsus can either refer to ‘exercise’ or ‘wear and tear’
- Fidēs nōn ad ūsum tendit: the insurance does not cover wear and tear.
- Musculōsa ūsū cotidiānō exstitit: she became very buff through daily exercise
- (the more straightforward exercitātiō is more common, at least in my experience)
3. It can also reference a ‘habit’ or social ‘custom’
- ūsum loquendī populō concessī; scientam mihi reservāvī: I have give up my habit of making speeches to the people, but I have retained my habit of learning (Cicero in old age)
- populum auctōritāte suā ad ūsum frūgalitātis vocāvit: by his authority, he brought the people to a habit of moderation (Lycurgus)
The phrase ūsus est + ablative is the rarer counterpart to the well known opus est + ablative, signifying need.
- Nunc vīribus ūsus est: now there is need of strength.
- Quid istīs cōnscrīptīs ūsust: what is the use of getting these in writing?
Ūsus vēnit is another still rarer alternative.
The Essential AG: 411