Green’s Dictionary of Slang

1. (US) a giver, usu. of money.

1901

‘Hugh McHugh’ Down the Line 42: He’s such a stingy loosener that he looks at you with one eye so’s not to waste the other.

2. (US) in pl., prunes [their trad. role in curing constipation].

1925		J. Stevens ‘Logger Talk’ AS I:3 137/2: For dessert he ‘takes on’ ‘open-face pie’ or ‘pie with the bark on’, some ‘choker holes (doughnuts),’ a dish of ‘looseners (prunes)’, a ‘slab’ of cake, and a ‘top load’ of Java.
1936		H.W. Bentley ‘Linguistic Concoctions of the Soda Jerker’ in AS XI:1 44: LOOSENERS. Prunes.