Old English hæsl, hæsel, from Proto-Germanic *hasalaz (source also of Old Norse hasl, Middle Dutch hasel, German hasel), from PIE *koselo- "hazel" (source also of Latin corulus, Old Irish coll "hazel"). Shakespeare ("Romeo and Juliet," 1592) was first to use it (in print) in the sense of "reddish-brown color of eyes" (in reference to the color of ripe hazel-nuts), when Mercutio accuses Benvolio:

Thou wilt quarrell with a man for cracking Nuts, hauing no reason, but because thou hast hasell eyes.

Proto-Indo-European root meaning "hook, tooth."

It forms all or part of: hacek; hack (v.1) "to cut roughly, cut with chopping blows;" hake; Hakenkreuz; heckle; hook; hooker.

It is the hypothetical source of/evidence for its existence is provided by: Russian kogot "claw;" Old English hoc "hook, angle."

Old English hacele "coat, cloak, vestment, mantle" (cognate with Old High German hachul, Gothic hakuls "cloak;" Old Norse hekla "hooded frock"), of uncertain origin. The same word with a sense of "bird plumage" is first recorded early 15c., though this might be from unrelated Middle English hackle "flax comb" (see heckle (n.)) on supposed resemblance of comb to ruffled feathers, or from an unrecorded continental Germanic word. Metaphoric extension found in phrases such as raise (one's) hackles (as a cock does when angry) is by 1881.

mid-15c., "one who uses a heckle" (late 13c., as a surname, Will. le Hekelere), agent noun from heckle (v.). Sense of "audience member that taunts a public speaker" is from 1885. Fem. form hekelstere is attested from c. 1500.

formerly also teaze, Old English tæsan "pluck, pull, tear; pull apart, comb" (fibers of wool, flax, etc.), from Proto-Germanic *taisijan (source also of Danish tæse, Middle Dutch tesen, Dutch tezen "to draw, pull, scratch," Old High German zeisan "to tease, pick wool").

The original sense is of running thorns through wool or flax to separate, shred, or card the fibers. The figurative sense of "vex, worry, annoy" (sometimes done in good humor) emerged 1610s. For similar sense development, compare heckle. Hairdressing sense is recorded from 1957. Related: Teased; teasing; teasingly.