treater

treat +‎ -er

treater (plural treaters)

1. One who or that which treats.
   • 2014, Martin Fleishman, The Casebook of a Residential Care Psychiatrist, page 58:

     I don't know why I do things like that except that sometimes I think that the principal difference between the treater and the treatee is that the treater is in possession of the keys, if only in a symbolic sense […]

2. A vessel used to treat oil-water emulsions by any of several mechanisms so that the oil can be accepted by the pipeline or transport.

• heat treater
• trick-or-treater

• Schlumberger Oilfield Glossary

• re-treat, retreat, tree rat