From arm +‎ hook.

armhook (plural armhooks)

1. A hook-like projection on the arm of a cephalopod, such as on the armhook squid (Gonatus fabricii).
   • 1977, Videnskabelige meddelelser fra Dansk naturhistorisk forening:

     In Ancistrotheutis the attachment ring persists, and the hook sac surrounding the tentacle hook is closed except during function contrary to the condition in the armhooks where the hook always projects from the sac.

   • 1988, Rapport: - Issues 140-142, page 101:

     The bivalve Posidonia permica frequently occurs in large concentrations on slabs of the shale in which there are also concentrations of cephaloped prehensile armhooks representing no doubt distorted natural assemblages from single individuals.

   • 1989, Norbert Schmidt-Kittler, Rainer Willmann, Phylogeny and the Classification of Fossil and Recent Organisms:

     Furthermore the armhooks of the Belemnoidea show a micro-texture and a mode of growth similar to the horny inner rings of the suckers of the Decabrachia.

2. (folk dancing) A movement in which two people hook arms at the elbow and turn around each other.
   • 1908, Jakob Bolin, Swedish Song-plays:

     When the partners meet they form armhook with each other, turn around once, let go, and continue the march till they again meet, when they march up into straight flank formation and halt at the end of the stanza.

   • 1915, Elizabeth Burchenal, Folk-dances of Denmark: containing seventy-three dances, page 66:

     With a clap the first and second men take right armhook with own ladies, then left with each other, right with own ladies, then left with each other, and retire to the same places as at the finish of part A ;

3. A hook for maneuvering something using the arm.
   • 1919, Architecture and Building - Volume 51:

     By the arrangement of these armhooks, it is possible for nurses to open doors while both hands are occupied.

   • 1938, Lockie Parker, Story Parade - Volume 3, page 17:

     The pushcarts and automobiles may be single painted cardboards inserted on wooden runners. The automobiles may be moved across the stage by a player behind the cardboard. A cloth armhook will hold it steady.

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