Webster's English Dictionary

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rachis

ra.chis \'ra--k*s, 'rak-*s\ \'rak-*-.de-z, 'ra--k*-\ n or ra.chis.es also 
   ra.chi.des [NL rachid-, rachis, modif. of Gk rhachis] pl  1: SPINAL COLUMN  
   2: an axial structure : as  2a1: the elongated axis of an inflorescence  
   2a2: an extension of the petiole of a compound leaf that bears the leaflets 
    2b: the distal part of the shaft of a feather that bears the web