1. [n]  a substance used to provide cooling (as in a refrigerator)
2. [adj]  causing cooling or freezing; "a refrigerant substance such as ice or solid carbon dioxide"

REFRIGERANT is a 11 letter word that starts with R.

1. \Re*frig"er*ant\ (r?*fr?j"?r-ant), a. [L.
   refrigerans, p. pr. of refrigerare: cf. F. r['e]frig['e]rant.
   See {Refrigerate}.]
   Cooling; allaying heat or fever. --Bacon.
   
   

2. \Re*frig"er*ant\, n.
   That which makes to be cool or cold; specifically, a medicine
   or an application for allaying fever, or the symptoms of
   fever; -- used also figuratively. --Holland. ``A refrigerant
   to passion.'' --Blair.