These words all mean to become or remain closely and firmly attached. Stick and adhere express the idea of maintaining a close or permanent union by or as if by gluing or cementing together. Stick is the less formal word of the two and conveys in addition the establishing of such an attachment: two young men who intend to stick together when they enter the armed services; to stick a label on a package. Stick may also imply perseverance, as in working at something or in keeping to an ideal, bargain, etc.: sticking doggedly at his physics homework until long after midnight; sticking to his principles of fair play; sticking to an agreement made in a moment of optimism. Adhere , which is always used intransitively, may sound formal and stiff when applied to things: a stamp adhering to a postcard.

Cohere , also an intransitive, refers to the adhering or sticking together of the particles of a substance, which then form a resultant whole or mass that is resistant to separation: Plaster of Pairs coheres only when water is added. Figurative usage may indicate the achievement of logical consistency: An argument coheres only if it validly bridges the premise and the conclusion.

Cling is used to indicate a close attachment caused by entwining, clutching or hanging on, rather than by gluing or otherwise causing surfaces to adhere: ivy clinging to brick walls; a baby koala clinging to its mother by clutching her fur. In the sense of holding on to attitudes, beliefs or emotional states, cling used as a synonym for adhere often has derogatory connotations suggestive of the presence of anxiety or dependency: a widow clinging to her grown son; people who, despite obvious intelligence, persist in clinging to old prejudices.

Cleave , in the sense of adhere or stick , is now largely a literary or Biblical term for being closely attached, as in a human relationship marked by fidelity: to cleave to one’s marriage partner through sickness and misfortune. In a few contexts, cleave is still used to mean literally to adhere or stick closely: In his terror his tongue seemed to cleave to the roof of his mouth.