The answer is HACHURE
The corresponding square is SHORT LINE RR
   by Dave Savitt

Each word is a unistem, from scrabble: there is a single letter that
can be added to the word and rearranged to form a new word.  There are
36 words, six groups of six.  Taking the added letters in groups of
six, the same property applies (add one letter, rearrange to form a
word).  The final set of letters added also have this property, and by
adding an 'e', the answer is given.

NOTE: the 6 word groups are not in this order (though they are ordered
as shown in their groups).


   muscly -> e (lyceums)
   ablush -> f (bashful)
   caulks -> f (sackful)
   queasy -> k (squeaky)
   laughs -> o (goulash)
   busses -> t (subsets)
------------------------
   getups -> a (upstage)
   wafery -> e (freeway)
   thumbs -> i (bismuth)
   crafty -> o (factory)
   yeoman -> r (anymore)
   feisty -> t (testify)
------------------------
   mimics -> a (miasmic)
   sultry -> i (rustily)
   canopy -> m (company)
   grooms -> p (pogroms)
   lodged -> s (dogsled)
   arcana -> v (caravan)
------------------------
   joules -> a (jealous)
   squibs -> e (bisques)
   storms -> i (missort)
   droopy -> s (prosody)
   lonely -> v (novelly)
   pretax -> y (apteryx)
------------------------
   barman -> d (armband)
   peaked -> n (kneepad)
   tomato -> n (ottoman)
   layman -> o (anomaly)
   mopped -> o (popedom)
   capons -> w (snowcap)
------------------------
   vortex -> a (overtax)
   drowsy -> b (bywords)
   fluors -> e (ourself)
   razzes -> j (jazzers)
   cystic -> l (cyclist)
   fivers -> y (versify)
------------------------
   effkot -> a (takeoff)
   aeiort -> c (erotica)
   aimpsv -> h (vampish)
   aeisvy -> h (yeshiva)
   dnnoow -> r (nonword)
   abejly -> u (bluejay)
------------------------
   achhru -> e (hachure)

and the answer to the puzzle is HACHURE