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Work out in the ring (4 letter answer)
The answer SPAR is very common and appears about once every 49 puzzles.
Box for a drill
Go a round
Practice in the ring
Prepare for a bout
Train for a bout
Train in a ring
Go a few rounds
Jack yard or gaff
Practice a la Marciano
SPAR as a noun:
1. any of various nonmetallic minerals (calcite or feldspar) that are light in color and transparent or translucent and cleavable
2. a stout rounded pole of wood or metal used to support rigging
3. (spar, sparring) = making the motions of attack and defense with the fists and arms; a part of training for a boxer
SPAR as a verb:
1. furnish with spars
2. fight with spurs; "the gamecocks were sparring"
3. box lightly
4. fight verbally; "They were sparring all night"