reliable (adj.) Look up reliable at Dictionary.com
1560s, raliabill, Scottish; see rely + -able. Not common before 1850; and sometimes execrated thereafter in Britain as an Americanism because it involves a use of -able different from its use in provable, etc., but defended (by OED, Century Dictionary, etc.) on grounds of use of the suffix in available, laughable, etc.. Related: Reliably.