Sanctimonious, a. — Webster enters it under “sanctimonious”
Etymology: [See Sanctimony.]
1. Possessing sanctimony; holy; sacred; saintly. Shak.
2. Making a show of sanctity; affecting saintliness; hypocritically devout or pious. "Like the sanctimonious pirate." Shak. -- Sanc`ti*mo"ni*ous*ly, adv. -- Sanc`ti*mo"ni*ous*ness, n.
Shades of meaning
Fernald has no entry of its own for sanctimoniousness; he lists it under hypocrisy.
Where he writes about it:
Cant (L. cantus, a song), primarily the singsong iteration of the language of any party, school, or sect, denotes the mechanical and pretentious use of religious phraseology, without corresponding feeling or character; sanctimoniousness is the assumption of a saintly manner without a saintly character. — from hypocrisy
As cant is hypocrisy in utterance, so sanctimoniousness is hypocrisy in appearance, as in looks, tones, etc. — from hypocrisy