an accepted or professed rule of action or conduct

a person of good moral principles.

a fundamental, primary, or general law or truth from which others are derived

the principles of modern physics.

a fundamental doctrine or tenet; a distinctive ruling opinion

the principles of the Stoics.

principles, a personal or specific basis of conduct or management

to adhere to one's principles; a kindergarten run on modern principles.

guiding sense of the requirements and obligations of right conduct

a person of principle.

an adopted rule or method for application in action

a working principle for general use.

a rule or law exemplified in natural phenomena, the construction or operation of a machine, the working of a system, or the like

the principle of capillary attraction.

the method of formation, operation, or procedure exhibited in a given case

a community organized on the patriarchal principle.

a determining characteristic of something; essential quality.

an originating or actuating agency or force

growth is the principle of life.

an actuating agency in the mind or character, as an instinct, faculty, or natural tendency

the principles of human behavior.

Chemistry . a constituent of a substance, esp. one giving to it some distinctive quality or effect.

Obsolete . beginning or commencement. ?

in principle

in essence or substance; fundamentally

to accept a plan in principle.

on principle

according to personal rules for right conduct; as a matter of moral principle

He refused on principle to agree to the terms of the treaty.

according to a fixed rule, method, or practice

He drank hot milk every night on principle.

noun

assumption , axiom , basis , canon , convention , criterion , dictum , doctrine , dogma , ethic , form , formula , foundation , fundamental , golden rule , ground , maxim , origin , postulate , precept , prescript , principium , proposition , regulation , rule , source , theorem , truth , usage , veritynotes:principle means fundamental , as in beliefs or truths or understandings and it is always a noun; principal can be a noun or adjective meaning chief or of first importance , universal , fiber , honesty , integrity , alpha and omega , belief , code , constitution , credo , creed , decalogue , declaration , element , essence , ethics , fundament , gospel , honor , law , methodology , morals , motto , organon , philosophy , quintessence , standards , substratum , teaching , tenet , theory , uprightness