Adherence, n.
Etymology: [Cf. F. adhérence, LL. adhaerentia.]
1. The quality or state of adhering.
2. The state of being fixed in attachment; fidelity; steady attachment; adhesion; as, adherence to a party or to opinions.
Syn. -- Adherence, Adhesion. These words, which were once freely interchanged, are now almost entirely separated. Adherence is no longer used to denote physical union, but is applied, to mental states or habits; as, a strict adherence to one's duty; close adherence to the argument, etc. Adhesion is now confined chiefly to the physical sense, except in the phrase "To give in one's adhesion to a cause or a party."
Shades of meaning
Fernald has no entry of its own for adherence; he lists it under attachment.
Where he writes about it:
An attachment is a feeling that binds a person by ties of heart to another person or thing; we speak of a man's adherence to his purpose, his adhesion to his party, or to anything to which he clings tenaciously, tho with no special tenderness; of his attachment to his church, to the old homestead, or to any persons or objects that he may hold dear. — from attachment