Steal, pilfer, filch, purloin, lift, pinch, snitch, swipe, cop are comparable when they mean to take another’s possession without right and without his knowledge or permission.
Steal, the commonest and most general of the group, can refer to any act of taking without right, although it suggests strongly a furtiveness or secrecy in the act.
Pilfer suggests stealing in small amounts or with cautious stealth and often bit by bit.
Filch is close to pilfer but may suggest more strongly the use of active though surreptitious means, especially quick snatching.
Purloin usually shifts the stress onto the idea of removal or making away with for one’s own use, often becoming generalized to include such acts as plundering or plagiarism.
Lift, when it does not mean specifically to steal by surreptitiously taking from counters or displays in stores, is used frequently in spoken English in the sense of purloin .
Pinch , swipe , snitch , and cop are virtually interchangeable with filch .
Pinch and swipe are often used in place of steal to suggest an act morally less reprehensible or sometimes more dashing and occasionally to suggest a petty meanness.
Snitch possibly stresses more the removal by quick, furtive snatching.
Cop usually lays stress upon quick, often spur-of-the-moment filching or purloining.