ETYM Cf. French partitif.
1. Serving to separate or divide into parts; SYN. separative.
2. Indicating or characterized by or serving to create partition or division into parts.
3. (Romance languages) Relating to or denoting a part of a whole or a quantity that is less than the whole.

A word (such a 'some' or 'less') that is used to indicate a part as distinct from a whole.
Indicating a part of a larger whole