For financial status:
* Impoverished
* Indigent
* Destitute
* Needy
* Underprivileged
* Low-income
* Deprived
* Penniless
* Broke
* Struggling
For quality or condition:
* Inferior
* Substandard
* Mediocre
* Unsatisfactory
* Lackluster
* Second-rate
* Unremarkable
For a person's character:
* Miserable
* Unfortunate
* Pitiful
* Wretched
* Pathetic
For something lacking:
* Deficient
* Sparse
* Scanty
* Limited
* Insufficient
Please provide more context about how you're using the word "poor" so I can give you a more specific synonym.