### Clue: Small bottle of very acidic beer unfinished (5)
### Answer: PHIAL 
 ### Explanation: Definition: Small bottle
 PHI(pH1 with the Roman numeral substitution – in chemistry, the acidity or alkalinity of a solution is measured on the pH scale with pH1 being very acidic) + "ale"(a type of beer) **minus ****its last letter**(unfinished).