Late 19th century; earliest use found in Encyclopaedia Britannica. From classical Latin prōclīnāre to cause to lean forward, to incline + -ing, apparently after inclining.
Definition of proclining in US English:
proclining
adjectiveprə(ʊ)ˈklʌɪnɪŋ
rare
Tilted, angled, or leaning forward.
Origin
Late 19th century; earliest use found in Encyclopaedia Britannica. From classical Latin prōclīnāre to cause to lean forward, to incline + -ing, apparently after inclining.